I'm assuming you have:
from django.contrib.localflavor import us
somewhere before you try to define phone_number as us.forms.USPhone...
Instead try:
from django.contrib.localflavor.us.forms import USPhoneNumberField
phone_number = USPhoneNumberField()
This works for me. I don't know why the documentation (
http://www.djangoproject.com/documentation/localflavor/) shows an example using the first kind of import, since it does not appear that things are set up for that to work.
Karen