They can tell which sector the phone pinged on, on a single tower. Which gives them a general direction. It is not one gigantic circle.
They just can't triangulate from one tower, or two (although two is better than one, and not as good as three or more). And the sector is rather large.
I have posted this link several times now. I think it is one of the easiest explanations for a layperson to understand.
Here is how a single mobile network tower would work.
The mobile tower can determine that the signal is being received from the γ sector, and that the source of the signal is close to 8 km from the mobile tower.
The mobile tower is then able to locate the source of the signal, placing the device within the yellow band which is around 16km long and .25km wide for a total of around 4km².
Within each sector, the tower can determine the distance of the transmitting device. This is done by measuring the strength of the signal and the time in which it takes for the signal to hit the destination and return.
View attachment 529531
Cell Tower Triangulation is a technique used widely by mobile network operators, devices and phones to help identify their location. A device that is within communication range of three or more mobile network towers is located by the overlap of signals based upon its range from each tower.The...
www.gpyes.com.au