All received and missed calls are sent to Google Analytics as "Events"
You can see them in the Behavior tab of Google analytics under:
(Click on) Events –> Top Events.
From the list, select “call tracking” as shown in the image below:
This allows you to see your call tracking events by keyword, country, region and a lot of factors by selecting it as a secondary dimension
This allows you to see which keywords are actually converting to calls.