GrapheneOS

This looks promising, and is targeted towards only the Pixel phones. Definitely tempted to try it when I get the chance.

I think the same general concept holds true. Generally be definition having a cell phone plan your carrier is going to know where you are, and your call records. But the only way to make the contents of your phone private is to use an open source option, where you can inspect and read the code, compile it if you need to, so you know specifically what's running on your phone.

The only other concern is if there is any kind of bios level spyware build directly into the cpu or other hardware.