Community Forum
So you seem to have a mobile phone number that's your Xfinity ID, that's not tied to your current Xfinity ID that you're signed into the forums with (which may be associated with your gmail). Use your mobile phone number to sign in, then go to My Account --> Users, and invite a user and send that to your gmail, and you can pull the gmail off of your other identity and put it on your primary where you've got your mobile phone number.
For anyone else seeing this, please use the www.xfinity.com/id lookup functionality to confirm your correct Xfinity ID.