Confusing formatting in sign-up fields

[vincenthang]

The formatting of the fields in the sign-up page is not fully communicated to the user. (e.g. Phone Number should have transparent text stating how the number should be formatted.)

We should change the in-place text of the phone number field to:
Phone Number (e.g. 1234567890)
or add in-place hyphens as the number is typed

Similarly, to the other fields.