With the release of iOS 8 and OS X Yosemite, iPhone, iPad and Mac connected like never before: the unbelievable feature of Continuity allows you to make and receive iPhone calls on every Mac and iPad you own! However, it can also be a nuisance as people that you share iCloud account with would get iPhone calls on their iOS devices as well. Then, you can follow the 2 tutorials below to learn how to disable iPhone calls on iPad, iPod Touch and Mac.
If you just want your iPhone being used as phone, you can go to Settings >> FaceTime and toggle the iPhone Cellular Calls off to stop iPhone from forwarding phone calls to all iOS devices.
If you want to take advantage of Continuity just on iPad, iPod Touch 5th or Mac instead all of them, you can set iPhone up via the operations below to meet your needs.
Open Settings on your iPad, iPod Touch 5th or other iPhone that you don't want to receive calls synchronously and tap on FaceTime, then toggle iPhone Cellular Calls off to turn off the feature of Continuity.
Launch FaceTime app on Mac first, then click FaceTime and Preference in turn. After that, uncheck iPhone Cellular Calls under the Settings tab.