In the new OS X Yosemite, you can quickly start (and answer) phone calls using FaceTime on Mac. Your iPhone can be in your pocket or a bag across the room, as long as it’s within bluetooth range.
In my examples, I right-clicked a phone number I jotted down in Stickies. But you can also click the phone icon next to any number in Contacts. This should work in Safari pages and just about any other app as well.
If you’re looking to enable or disable this option, open the FaceTime app and go to preferences.