Turn off old iCloud number
Turn off delete old phones in existing iCloud and phone
iPhone 14 Plus, iOS 17
Whose device is this?
On your iPhone or iPad
Go to Settings > [your name] > Sign-In & Security. Next to Email & Phone Numbers, tap Edit. next to your phone number and follow the instructions. After you've entered the mobile phone number that you want to use as your Apple ID, a verification code will be sent to you on that number.