So why do Google Play Services, etc. have full privileged access to a phone, including private data and phone call audio, but the user doesn't?

It is tech feudalism - you don't own anything anymore, you just get to live on the digital land of a bunch of ~trillion dollar companies.

At least, that is the goal.

IMO either everyone gets access at the user's discretion or Google has to sandbox their own GMS services as well.

  Quod licet Iovi, non licet bovi