Open FaceTime on your Mac
Sign in with the same Apple ID used on your iPhone
On your iPhone, go to Settings
Tap FaceTime
Turn off FaceTime on your iPhone
On your Mac, go to FaceTime > Settings
Make sure your phone number and email addresses are checked
On your Mac, choose FaceTime > Settings > iMessage/FaceTime preferences if needed
Set your Mac as the default device for FaceTime calls
Use your Mac to make and receive FaceTime calls