All received and missed calls are sent to Google Analytics as "Events"

Youu can see them in the Behavior tab of Google analytics under:

(Click on) Events –> Top Events.

From the list, select “calltracking” 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 (as shown below).

This allows you to see which keywords are actually converting to calls.