Forgot Phone Number

If the number is on your Apple ID, can you sign into your ID to see what the number is?

Apple ID - Manage   

If the number is on your Apple ID, have you tried signing out of Messages, restarting your device, and signing back in to see if the number on your Apple ID will show?

Have you tried checking Messages/FaceTime to see if the number shows there?

Did you try signing into your Apple ID to see what number is listed there?