how to change phone number on iPhone for apple id

See:

If you can't send or receive messages on your iPhone, iPad, or iPod touch https://support.apple.com/en-us/HT204065

If you get an error when trying to activate iMessage or FaceTime https://support.apple.com/en-us/HT201422

Use your mobile phone number as your Apple ID https://support.apple.com/en-us/HT207944#change-appleid. See the heading Change your Apple ID to a different mobile phone number.

If you are trying to change the number used by Messages/FaceTime, you need to change the number on your Apple ID. After the change, allow up to 24 hours for the change to sync. Before trying to make the change, sign out of Messages/FaceTime.

Apple ID - Manage