Mobile phones use GPS, to be sure, but they also discern location by WiFi radio locations. If your phone is connected to BigCorpWiFi, then we know where you are. Even if you are in the BigCorp building connected to BigCorpWiFi with SmallCorpWiFi from next door detectable, we know which side of the building of BigCorp you are located. If you're on the street corner and your phone can see the WiFi networks of WiFi-1, WiFi-2, WiFi-3, we now know which street corner you are on without accessing the GPS chip. If the WiFi-2 signal is stronger, we know which side of the street you are on.

Forget WiFi. Walking down a street with lots of retail shops while Bluetooth is enabled receives pings from all sorts of trackers/beacons. We know where you are.

TL;DR: If you think location data is only discernible by using GPS, you are incorrect.