Go to My Account and in the Users tab click “add new user” and invite them using the phone number. You’ll get a text and simply click on the link and confirm your address and link your accounts. You can then remove the phone number from that account and add it to your existing user.
This is a temporary solution before we enable mobile phone number moves in Q4.
If you are still having issues feel free to PM me
I am an Official Comcast Employee (On the HQ Identity Product and Serviceability Teams). Official Employees volunteer their time outside of their normal day jobs to create the best customer experience possible. If and only if you've been tagged, you can PM us by clicking on our name and clicking "Send a Message"