Add new phone number to MacBook Pro
How do you change an email on your MacBook Pro to the phone number you have on your iPhone so that all the texts are the same on both.
MacBook Pro 13", macOS 10.14
Add or remove your phone number in Messages or FaceTime - Apple Support
On your Mac...Try...System Preferences...iCloud...Account Details...Contact...add your number.
If that does not help see the last line in the above link which says...If you still need help, change your Apple ID password and repeat the setup steps. If that doesn't work, contact Apple Support.