In v. 4.1.3 I notice that the user profile form does not include phone data. However there is a phone field in the distribution user database. Is this field used for anything (like getting a phone number from Paypal passback data, say) or can I steal it for my user phone numbers?
Yes, that field is for user phone number, and is not used by aMember at all. We will make a standard brick for it, so it can be used in signup/profile forms.