Hello unknown7o7,
Welcome to Apple Support Communities. I understand that you want to change the phone number the you use for FaceTime on your MacBook Pro.
On your MacBook Pro, please open the FaceTime app. Go to Preferences > Settings. In Settings, it should show your Apple ID signed in. If it doesn’t, then sign out of that Apple ID and sign in to your Apple ID. If you have an iPhone and sign in to the MacBook Pro with that same Apple ID, you will be able to be reached at that phone number and your Apple ID on your MacBook Pro as well.
Here’s some information on using FaceTime on your Mac: Use FaceTime on your Mac - Apple Support
Here’s information regarding Continuity on your Apple devices: Use Continuity to connect your Mac, iPhone, iPad, iPod touch, and Apple Watch - Apple Support
If you still need help, please click contact Apple Support by clicking Contact Support in the upper right here: MacBook Pro - Official Apple Support
Cheers.