How to write the pattern attribute of an input telephone number in HTML?

The question is as :

• The Telephone input field type should be 'tel',
• The placeholder text should be Pattern: 234-567-8910
• The pattern to restrict the entry and it should be a mandatory (required) field
• Pattern should be of the type [ Pattern: 234-567-8910].
• Element name should be: telephone.

My code is

<input type="tel" name="telephone" id="telephone" required placeholder="Pattern: 234-567-8910" pattern="">

What to write in the attribute pattern ?

The pattern in an input would take a regular expression. Your requirement is to get a regex what would fit in the requirement [ Pattern: 234-567-8910].

The regex would be

 pattern="[0-9]{3}-[0-9]{3}-[0-9]{4}"