Change my phone number

Usually. I just did that. but the guy at the store said that there were a few exchanges in  our area that it wan't possible. I went into a local store and the guy there did most of it. I wasn't interested in changing to Xfinity Internet/Voice unless I could port the phone number.

It took a couple of days without phone service to "port" the number. The story I got from a person at the ATT call center was that the ATT account has to be active. then the requesting service (Xfinity) makes the port request for a certain date, when the request is approved, the phone quits working until the requested date comes along and it can be activated. Didn 't make a lot of sense to me, but it was their story and they stuck to it.

According to Comcast's documentation, you should have been given the option to port the phone number over when signing up for service.  The number portability FAQ is available here:

https://www.xfinity.com/support/articles/local-number-portability

If it is an U-verse Voice phone number then I *think* you should be able to port it as long as AT&T phone service is still active.

If it is a classic land line then it might not be eligible for number portability.

If you have any Google account, such as gmail, you should be able to activate Google Voice service.  They then provide access to an online live Port Status check as the first step of attempting to port a number.  This can give you information on if the number you are trying to port is eligible or not.  You don't have to continue past the first step of the process making it possible to use GV only for performing the check and nothing else.