Ajlok I actually think that you would be at a disadvantage trying to use an apple device as a hotspot to mitigate anything. Apple OS contains code that nobody knows about except the people at apple and those they share it with under NDA, which probably includes some governments and service providers, so the amount of tracking possible is virtually unlimited.
To me it looks like the only problems you are having is with respect to spam calls, and occasionally being called by the service provider. Spam calls are not necessarily a function of anything except random chance. A lot of spammers simply go through phone numbers by guessing at random numbers and seeing who answers and what numbers don't exist. That means that even if you have a VoIP number for your phone calls, you'll STILL be subject to spam calls. There's really nothing you can do about that except go entirely without a phone that can make calls.
If you wanted to go without a phone that can make calls, you can simply disable calling on the phone, or get a data-only sim card.
Really all you would do by adding an additional device into the mix, is INCREASE your attack surface.