If you tried tapping the call button to make a phone call, but nothing happens, the quickest solution is to kill or close the Phoner app and then relaunch it again.
To kill or close the Phoner app:
- Open the Phoner app
- Kill the app, making sure that it is cleared from your phone's running apps
- Reopen the Phoner app
- Make a phone call and you should be able to dial out to your intended contact.
See How to fix app crashing, or app not responding? for more detailed screenshots. In many cases it should work, unless you do not have a stable and active Internet connection or cellular connection.