Cell towers require precise timing for a variety of reasons and phones can synchronise to that time source. Phone clocks are good enough that as long as you don

Cell towers require precise timing for a variety of reasons and phones can synchronise to that time source. Phone clocks are good enough that as long as you don't go too long between seeing cell towers then your signal isn't going to have walked too much. The way they're using them, it sounds like 1 second resolution is easily sufficient. That would be achieved by a 1 ppm accuracy crystal (fairly standard) that is synchronised once a week.