I have an article here that I believe will help you with this question:
To remove a phone number from an Apple ID, sign out of FaceTime and Messages on your iPhone:
- Settings > Messages > Send & Receive. Tap your Apple ID, then tap Sign Out.
- Settings > FaceTime. Tap your Apple ID, then tap Sign Out.
This should remove your phone number from other devices using the same Apple ID with FaceTime and Messages. If the phone number is still available on other devices after you sign out of FaceTime and iMessage on the iPhone, you may need to sign out of iMessage and FaceTime on all your devices, then sign in to FaceTime and Messages again on devices you want to use.
Note: If you no longer have access to the iPhone that is using the number you want to remove, reset your Apple ID password.
Thanks for using the Apple Support Communities!