In the Call History list, you can see some phone icons. These icons shows the quality of the call and this is what means each one of them:
Call made with a good connection
Call made with Internet connection problems
Toky detected connection problems during the call that possibly affected voice quality. It is advisable to check the quality of your internet connection.
No call connection data
The call was canceled or did not last long enough to generate a quality report.
No audio during the call
No audio was detected from the caller or the agent, possibly due to microphone problems.