after high sierra 10.13.2 update iPhone calling doesn't working

Use Continuity to connect your Mac, iPhone, iPad, iPod touch, and Apple Watch - Apple Support

With the iPhone Cellular Calls feature, you can make and receive calls from your Mac, iPad, or iPod touch when those devices are on the same network as your iPhone.

Set up iPhone Cellular Calls

Use iPhone Cellular Calls with any Mac, iPhone, iPad, or iPod touch that meets the Continuity system requirements. It works when your devices are near each other and set up as follows:

• Each device is signed in to iCloud with the same Apple ID.
• Each device is signed in to FaceTime with the same Apple ID.
• Each device has Wi-Fi turned on.
• Each device is connected to the same network using Wi-Fi or Ethernet.
• On iPhone, go to Settings > Phone > Calls on Other Devices, then turn on Allow Calls on Other Devices.
• On iPad or iPod touch, go to Settings > FaceTime, then turn on Calls from iPhone.
• On Mac, open the FaceTime app, then choose FaceTime > Preferences. Click Settings, then select Calls From iPhone.

If your carrier supports Wi-Fi calling on other devices, you can set up those devices to make and receive calls even when your iPhone isn't turned on or nearby. Learn about Wi-Fi calling.

Use iPhone Cellular Calls

Make a call on your iPad or iPod touch

• Tap a phone number in Contacts, Calendar, Safari, or other app that automatically detects such data.
• Or open the FaceTime app and enter the phone number in the search field. Tap the phone number in the search result, then tap Call.

Make a call on your Mac

• Move the pointer over any phone number in Contacts, Calendar, Safari, or other app that automatically detects such data. Click the arrow in the box that outlines the phone number, then choose Call [phone number] Using iPhone.
• Or open the FaceTime app and enter a phone number in the search field. Control-click the phone number in the search result, then choose the phone number from the pop-up menu.

Answer a call

• On iPad or iPod touch, slide to answer the call.
• On Mac, a notification appears when someone calls your iPhone. From there you can answer the call, send it to voicemail, or send the caller a message.

To stop getting calls at one of your devices, just turn off the Calls from iPhone setting on that device. See the setup section above for details.

My brother has the same problem. He has iMac 27" 2017, and iPhone 7+ and can't make the phone call from iMac. i have the same iMac and iPhone 6 and it works.

Any idea what he might do to fix it? All systems are running latest OS. He has both iPhone and iMac set up correctly (same as me), but it doesn't work.

When he tries to call from iMac, it says that the call filed. When I calls him from iPhone, it appear on iMac, however, when he answer the call, it also fails in connection.

Any idea?

Sign out facetime on your phone, and sign out facetime on your mac. Then sign in again. That worked for me.