Phones go into an emergency mode where they transmit the gps location. The accuracy depends on factors including length of call iirc.

I believe they can then call the carrier to ping the phone to report location. Typically that happens if the dispatcher has reason to believe there is a emergency situation and the call drops.

I think the phone will notify you of this. At least it did many years ago when I called 911 for a car accident on the highway.