Three layers, cheapest first: Google's call assets and call reporting track calls from the ad itself; a Google forwarding number on your site tracks callers who clicked first; full call-tracking services (dynamic number insertion) tie every call to its source, keyword included.
The one setting that separates signal from noise: count only calls over a duration threshold (30-60 seconds) as conversions — wrong numbers and 'are you open' calls otherwise inflate everything.
If calls are your business's real conversion, this isn't optional plumbing: without call tracking, phone-heavy campaigns look like failures in the data while the phone rings — and get optimized into actual failure.