FaceTime phone call requirements
To make and receive phone calls on your Mac (OS X 10.9 or later required), make sure of the following:
Your iPhone has iOS 8 or later installed. See the Apple Support article Update your iPhone, iPad or iPod touch.
Your iPhone and Mac are on the same Wi-Fi network and connected to the internet.
Your iPhone and Mac are signed in with the same Apple ID and iCloud and FaceTime are turned on. See the Apple Support article Use Continuity to connect your Mac, iPhone, iPad, iPod touch, and Apple Watch.
Your iPhone and Mac have Wi-Fi Calling turned on. Wi-Fi Calling isn’t available on some Mac models.