How do i updatephone number if i used phone auth in my app?

In my Flutter app I use Firebase’s phone number authentication as my main form of authentication. After authenticating, I create a user in my users collection
But say one day a user want’s to change their phone number. How do I do this? Because I cannot simply change the user’s phone number in the document, because the phone number needs to be authenticated. And after authentication, the user gets a new authUID. Which should then be a new user?

Could someone explain the logic behind a user that wants to keep their profile details but change their number.