This person is so paranoid, that they believe that a cyberweapon developed by a private company in Israel that uses previously-unknown bugs in the most sandboxed messaging system you can get on a phone are going to be deployed against them, so they should not use the calling, texting, or any other "phone-like" functionalities of a phone.
They then distrust that the End to End Encryption is in-fact End to End, and then think that using Signal or something is more secure, when if a bug in a system more sandboxed than Signal was found (iMessage, which has BlastDoor which Signal does not have), it is more than likely that Signal has it's own zero-days in it, so you shouldn't be using that either.
That's paranoid, and if you are that paranoid (which, maybe you have a reason to be), your solution isn't well thought-through. You shouldn't be using a phone if you can help it.
Fun fact: having systemwide location services on, even if you don't enable it for any apps, means that your location is sent in realtime to Apple/Google at all times (via Wi-Fi triangulation data). It's not just passive GPS reception.
If you want actual location privacy, you'll want to leave location services off systemwide on your smartphone, and consider getting an offline GPS receiver device. Good car satnav devices from China are like $60 now, and include continent-wide maps, though you lose realtime traffic info, being offline.
- OpenCellID (offline): https://f-droid.org/en/packages/org.gfd.gsmlocation/
- Radiocells.org (optionally offline): https://f-droid.org/en/packages/org.openbmap.unifiedNlp/
- Déjà Vu (offline cache using Wi-Fi and cellular data): https://f-droid.org/en/packages/org.fitchfamily.android.deja...
- Mozilla Location Services (online): https://f-droid.org/en/packages/org.microg.nlp.backend.ichna...
UnifiedNlp is preinstalled on Android distributions that include microG. CalyxOS is the only one of these that supports relocking the bootloader with the developers' key:
I'm in the camp of pragmatic resistance to surveillance. I use browser plugins to block ads and cookies where it doesn't get in the way of reaching the content I want; I use Signal for messaging even though almost none of my recipients do; I disable location services except for things like Maps that actually need to know where I am; I turn off all the spyware I know about that's built into operating systems; etc. I'm not a tin-foil-hat-wearer; I'm not doing anything illegal that I need to hide; I'm just trying to push back in a small way against the erosion of privacy and rights that permeates everything electronic.
But the parent isn't paranoid. They really are watching. And we shouldn't be so complacent.