If an advertiser uses Google’s phone call conversion tracking feature, how are the calls tracked to their account?

The calls are tracked by the conversion name for the advertiser’s store.
The calls are tracked by a dynamically created Google forwarding number.
The calls are tracked by the phone number listed on the advertiser’s official store website.
The calls are tracked by the assigned Google Click Identifier (GCLID) set up in the advertiser’s account.