Azure B2C user flow without an email

We have a scenario where we need to integrate Azure B2C with one of our existing system, where the email is not a mandatory user field, we have only the mobile number of the user as a mandatory field. I am looking for ways to integrate azure B2C where i can give a username and an initial password for the first time, instead of email. And all the password reset scenarios will have to go through OTP or email, where it will be a users choice to give email to reset the password.

We are able to create the user through Graph API initially, but stuck with creating a user-flow where it will ask the username and password instead of email and password.

You can choose Username as local account types when configuring identity providers for Azure AD B2C in the Azure portal. In your Azure AD B2C tenant, select Identity providers, select Local account, and then select Username.

Then you need to select Local Account again in your user flow.