How to change your old phone from Apple ID

You need to change/add the number on your Apple ID. Look in the Security section when signed in online. You may have to add the new number before you can remove the old number. After the change, allow up to 24 hours for the change to sync. Before trying to make the change, sign out of Messages/FaceTime on all devices/computers.

Apple ID - Manage

Don't ever share private info like telephone numbers and emailadresses on a public forums like this

To remove your old phone number, try to slide on it and see if a delete option will appear

Try what I posted above. After making the change, you may have sign out and back in.