[Answered ]-Django Custom Authentication Backend does not work

Assuming that you have already included the custom backend in AUTHENTICATION_BACKENDS setting in settings.py file.

You can make a condition check that whether it is a phone no. or email using regex so:

import re
from django.contrib.auth import get_user_model


class CustomAuthBackend:
    def authenticate(self, request, username=None, password=None):
        UserModel = get_user_model()

        # Check whether username is an email address or phone number
        if re.match(r'^\+?\d{10,14}$', username):
            try:
                user = UserModel.objects.get(phone_number=username)
                if user.check_password(password):
                    return user
            except UserModel.DoesNotExist:
                return None
        else:
            try:
                user = UserModel.objects.get(email=username)
                if user.check_password(password):
                    return user
            except UserModel.DoesNotExist:
                return None

    def get_user(self, user_id):
        try:
            return get_user_model().objects.get(pk=user_id)
        except get_user_model().DoesNotExist:
            return None