It would be relatively difficult to add a physical GPS tracker to a modern phone. Also, it's unnecessary, the government just needs to take a note of the IMSI and/or IMEI and then use the cell tower records to track you (rather accurately I should add).

The problem is not the tracking inherent in the design of mobile telephony networks, which you can circumvent by using burner phones. The problem is for example abuse of tools such as cellebrite to gain warrantless access to your phone at various opportunities.

This is also why proper baseband isolation is important. Baseband firmware is unaudited and likely to have government backdoors.

If the government wants to surveil me, they'll have to put in some actual effort instead of just taking opportunities.