Make a phone call using Messages on Mac
You can make a phone call from your Mac using Messages if you have an iPhone with iOS 8 or later nearby. Calls are relayed through your iPhone, but you use your Mac microphone and speakers to communicate. Phone calls use mobile minutes. Mobile charges may apply.
Note: To make a phone call from your Mac, you need to be signed in to iCloud using the same Apple ID on both your iPhone and your Mac, and they must both be on the same Wi-Fi network. See Make and receive phone calls in FaceTime on Mac or the Apple Support article Use Continuity to connect your Mac, iPhone, iPad, iPod touch, and Apple Watch.
In the Messages app
on your Mac, in the top-right corner of a conversation, click Details, then click the Audio button 
.If there’s more than one number in the contact card, choose the number to call. If there’s only one number, the call starts immediately.