You can download the board schematics here:

https://wiki.pine64.org/index.php?title=PinePhone_v1.2

And see exactly what the switches turn on and off. Heck, if you are really paranoid, you can inspect the PCB and the schematics of the individual chips to ensure it does what it does.

The datasheets for the individual chips are here:

https://wiki.pine64.org/index.php/PinePhone

EDIT: This has it too: https://wiki.pine64.org/index.php/PinePhone_FAQ#What_are_the...