Yeah but a phone is also a device collecting tons of useful metadata - nearby towers,wifi routers, bt devices and even the most secured iPhones can be turned leaky with enough access.

Simply get into an iPhone of a known location based app gamer and then add a pokestop to a location. Even if the gamer gets picked up it won't be too suspicious since they'll have a history of going to lots of random locations. Even if the hack is detected by a suspicious organization, the phone will have transmitted the info out by the time they detect the hack.

This is just one poorly thought out scenario, there are lots of things you can do with phones nowadays - use them as collection tools, relays etc