Change Your iPhone Settings
You can turn off the Continuity feature that causes your incoming iPhone calls to ring elsewhere. The best way is to change the settings on your iPhone:
Stop Calls on iPad and Other iOS Devices
Changing the settings on your iPhone should take care of things, but if you want to be sure, do the following on your other iOS devices:
Stop Macs From Ringing for iPhone Calls
The change of the iPhone setting should have done the job, but you can be double sure by doing the following on your Mac:
Stop Apple Watch From Ringing
The whole point of the Apple Watch is to have it notify you of things like phone calls, but if you want to turn off the ability for the Apple Watch to ring when calls come in:
More on Continuity
Incoming calls show up on multiple devices due to a feature called Continuity. Apple introduced Continuity with iOS 8 and Mac OS X 10.10 and continues to support it in later versions of both operating systems. Continuity allows your devices to be aware of and interact with one another. The idea is you should be able to access all your data and do the same things on any device. One well-known example of this is Handoff, in which you start writing an email on your Mac and continue writing the same email on your iPhone. For Continuity to work, all the devices must be near one another, connected to Wi-Fi, and signed in to iCloud.
