To stop the iPhone from ringing your other devices with an incoming phone call, you need to visit the Settings of the iPhone which has the cellular connection that originally receives the phone call. You can also choose to selectively disable the ringing feature on other devices if you’d like to just opt a single device out.
- Open the Settings app on the iPhone and go to “FaceTime”
- Toggle the switch for “iPhone Cellular Calls” and flip it to the OFF position
- Exit out of Settings as usual