Flutter TextField, need to reposition the TextField label and solve label being always shown to focused position due to prefix

I'm trying to build a pixel-perfect design in Flutter that includes a TextField. The design requires the label to behave like this:

1. When the TextField is not focused and empty, the label should appear inside the input field as a placeholder.
2. When the TextField is focused, the label should move just above the input text but still inside the border, not at the top-left edge of the TextField (the default floating label position).

I need: I need to design a pixel-perfect UI according to the design below:

But I'm currently having this:

The Problem: I have a prefix widget (like a country code selector for a phone number) that is always visible. Because of this, the label behaves as if the TextField is always focused — it's always displayed in its floating position, even when the field is not focused or filled.

Current Code What I've tried: Here is the code that I've tried to get the target design.

TextField(
        keyboardType: TextInputType.phone,
        scrollPadding: EdgeInsets.zero,
        decoration: InputDecoration(
          floatingLabelBehavior: FloatingLabelBehavior.always,
          label: Text(
            'Phone number',
            style: TextStyle(
              color: AppColors.secondaryTextColor,
              fontSize: 12,
              fontWeight: FontWeight.w500,
            ),
          ),
          errorText: showError ? formState['phoneError'] : null,
          errorMaxLines: 2,
          errorStyle: const TextStyle(fontSize: 12),

          // Content Padding
          contentPadding:
              const EdgeInsets.symmetric(vertical: 16, horizontal: 12),

          // Prefix for country code
          prefix: IntrinsicHeight(
            child: Row(
              mainAxisSize: MainAxisSize.min,
              children: [
                CountryCodePicker(
                  onChanged: (country) {
                    formNotifier.updateCountryCode(
                        country.dialCode ?? '+91', country.name ?? 'India');
                  },
                  textStyle: const TextStyle(
                    fontSize: 16,
                    color: AppColors.primaryTextColor,
                    fontWeight: FontWeight.w600,
                  ),
                  initialSelection: formState['countryCode'],
                  favorite: const ['IN', 'BD', 'US'],
                  showFlag: false,
                  showDropDownButton: true,
                  alignLeft: false,
                  padding: EdgeInsets.zero,
                  flagWidth: 24,
                  builder: (country) => Row(
                    mainAxisSize: MainAxisSize.min,
                    children: [
                      Text(
                        country?.dialCode ?? '+91',
                        style: const TextStyle(
                          fontSize: 16,
                          fontWeight: FontWeight.w600,
                        ),
                      ),
                      Gap(8),
                    ],
                  ),
                ),
                const VerticalDivider(
                  thickness: 1,
                  width: 1,
                  color: AppColors.defaultBorderColor,
                ),
                const SizedBox(width: 8),
              ],
            ),
          ),

          // Suffix Icons for validation
          suffixIcon: showError
              ? const Icon(Icons.close, color: Colors.red)
              : isValid
                  ? const Icon(Icons.check, color: Colors.green)
                  : null,

          // Borders
          border: OutlineInputBorder(
            borderRadius: BorderRadius.circular(8),
            borderSide:
                const BorderSide(color: AppColors.defaultBorderColor),
          ),
          focusedBorder: OutlineInputBorder(
            borderRadius: BorderRadius.circular(8),
            borderSide: const BorderSide(
                color: AppColors.darkBackgroundColor, width: 2),
          ),
          enabledBorder: OutlineInputBorder(
            borderRadius: BorderRadius.circular(8),
            borderSide:
                const BorderSide(color: AppColors.defaultBorderColor),
          ),
          errorBorder: OutlineInputBorder(
            borderRadius: BorderRadius.circular(8),
            borderSide: const BorderSide(color: Colors.red, width: 1.5),
          ),
          focusedErrorBorder: OutlineInputBorder(
            borderRadius: BorderRadius.circular(8),
            borderSide: const BorderSide(color: Colors.red, width: 2),
          ),
        ),
        onChanged: (value) => formNotifier.updateField('phone', value),
      )

Looking at the UI you want to achieve, I don't think that is possible using the native Flutter TextField.

Try building a custom text field using Stack and manage the label manually with AnimatedPositioned.

Here is a simple reusable component you can expand on:

import 'package:flutter/material.dart';

class PhoneInputField extends StatefulWidget {
  final TextEditingController controller;
  final FocusNode? focusNode;
  final String label;
  final String countryCode;
  final bool showError;
  final bool isValid;
  final String? errorMessage;
  final ValueChanged<String>? onChanged;

  const PhoneInputField({
    super.key,
    required this.controller,
    this.focusNode,
    this.label = "Phone number",
    this.countryCode = "+1",
    this.showError = false,
    this.isValid = false,
    this.errorMessage,
    this.onChanged,
  });

  @override
  State<PhoneInputField> createState() => _PhoneInputFieldState();
}

class _PhoneInputFieldState extends State<PhoneInputField> {
  late final FocusNode _internalFocusNode;
  FocusNode get _focusNode => widget.focusNode ?? _internalFocusNode;

  bool get _hasText => widget.controller.text.trim().isNotEmpty;
  bool get _isFocused => _focusNode.hasFocus;

  @override
  void initState() {
    super.initState();
    _internalFocusNode = FocusNode();
    widget.controller.addListener(_refresh);
    _focusNode.addListener(_refresh);
  }

  void _refresh() => setState(() {});

  @override
  void dispose() {
    if (widget.focusNode == null) _internalFocusNode.dispose();
    widget.controller.removeListener(_refresh);
    _focusNode.removeListener(_refresh);
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    final borderColor = widget.showError
        ? Colors.red
        : _isFocused
        ? Colors.black
        : Colors.grey[400]!;

    final showIcon = !_hasText
        ? null
        : widget.showError
        ? Icons.close
        : widget.isValid
        ? Icons.check
        : null;

    return Column(
      crossAxisAlignment: CrossAxisAlignment.start,
      children: [
        Stack(
          children: [
            Container(
              height: 56,
              decoration: BoxDecoration(
                border: Border.all(color: borderColor, width: 1.5),
                borderRadius: BorderRadius.circular(8),
              ),
              padding: const EdgeInsets.symmetric(horizontal: 12),
              child: Row(
                crossAxisAlignment: CrossAxisAlignment.center,
                children: [
                  // replace with your own code dropdwon or text
                  Text(
                    widget.countryCode,
                    style: const TextStyle(
                      fontSize: 16,
                      fontWeight: FontWeight.w600,
                    ),
                  ),
                  //////
                  const VerticalDivider(width: 20, thickness: 1),
                  Expanded(
                    child: TextField(
                      controller: widget.controller,
                      focusNode: _focusNode,
                      keyboardType: TextInputType.phone,
                      decoration: const InputDecoration(
                        border: InputBorder.none,
                        isDense: true,
                        contentPadding: EdgeInsets.only(top: 18),
                      ),
                      style: const TextStyle(
                        fontSize: 16,
                        fontWeight: FontWeight.w500,
                      ),
                      onChanged: widget.onChanged,
                    ),
                  ),
                  if (showIcon != null)
                    Icon(
                      showIcon,
                      color: showIcon == Icons.check
                          ? Colors.green
                          : Colors.red,
                    ),
                ],
              ),
            ),

            AnimatedPositioned(
              duration: const Duration(milliseconds: 200),
              left: 66,
              top: _isFocused || _hasText ? 8 : 18,
              child: AnimatedDefaultTextStyle(
                duration: const Duration(milliseconds: 200),
                style: TextStyle(
                  fontSize: _isFocused || _hasText ? 12 : 16,
                  color: widget.showError
                      ? Colors.red
                      : _isFocused
                      ? Colors.black
                      : Colors.grey[600],
                  fontWeight: FontWeight.w500,
                ),
                child: Text(widget.label),
              ),
            ),
          ],
        ),
        const SizedBox(height: 6),
        if (widget.showError && widget.errorMessage != null)
          Text(
            widget.errorMessage!,
            style: const TextStyle(color: Colors.red, fontSize: 12),
          ),
      ],
    );
  }
}

And here is how you can use it in your form (checkout, profile, etc.):

PhoneInputField(
                controller: _controller,
                focusNode: _focusNode,
                countryCode: "+1",
                isValid: _isValid,
                showError: _showError,
                errorMessage: "enter valid phone number",
                onChanged: _validate,
              ),