Apple® iPad® - Turn Continuity Cellular Calling On / Off
Continuity features connect iPhone with your iPad, iPod touch, or Mac so they can work together as one. You can use your iPad to make phone calls using the cellular connection from your iPhone. For additional Continuity functionality such as Handoff, view these product details.
You must be logged in to the same Wi-Fi network and using the same Apple ID among all your devices to use cellular calling; check out this info for additional Continuity requirements.
From a Home page, navigate to: Settings > FaceTime.
Tap the Calls from iPhone switch to turn on or off .