How does a phone call get attributed to a marketing source?

The mechanism, stated plainly

Every tracking number is a mailbox. The platform holds a pool of numbers, hands one to a visitor's session, records which source that session came from, and forwards the call to your real line. When a call arrives on that number the platform already knows the story behind it. Nothing clever happens on the call itself; the work was done before the phone rang.

That is why attribution quality is decided by number coverage, not by call quality. A channel with no dedicated number is a channel with no attribution, no matter how good the reporting looks.

Where phone attribution breaks

• Saved numbers. A customer who saved your number two years ago dials the real line. The call has no session behind it.
• Your Google Business Profile. Calls placed from the map pack use whichever number is listed there, and often land on one bucket for all local discovery.
• Screenshots and forwards. A tracking number captured in a screenshot and texted to a spouse can produce a call weeks later that is credited to the original session.
• Pool exhaustion. If concurrent visitors exceed the number pool, two sessions share a number and the platform has to guess.
• Duration thresholds. Most platforms only count a call as a lead past a minimum length, which quietly excludes short but real calls.

Attribution stops at the call, and that is the problem

Knowing that a call came from a campaign tells you nothing about whether it was a customer, a vendor, a wrong number or a job that booked. Call volume by source is a media metric. Booked revenue by source is a business metric, and getting from one to the other requires joining the call record to the job record.

Call analysis closes part of that gap by reading the conversation itself, so you can separate genuine service inquiries from noise before anyone counts leads. The rest is record matching into the operational system that holds the invoice.

A practical coverage checklist

Before you trust any call report, confirm four things: every paid channel has its own number, the website performs a dynamic swap for organic and paid sessions, offline and print placements each carry their own static number, and someone reviews the unmatched call bucket monthly. Most call attribution problems are coverage problems, and coverage problems are fixable in an afternoon.