Go to Settings > [your name] > Name, Phone Numbers, Email.
Next to Reachable At, tap Edit.
Tap Delete next to your phone number and follow the instructions.
After you enter the mobile phone number that you want to use as your Apple ID, a verification code is sent to you at that number. Enter the verification code from the text into the fields provided.
Go to Settings > [your name] > Name, Phone Numbers, Email.
Next to Reachable At, tap Edit.
Tap Delete next to your phone number and follow the instructions.
After you enter the mobile phone number that you want to use as your Apple ID, a verification code is sent to you at that number. Enter the verification code from the text into the fields provided.