LineageOS (https://lineageos.org/) on a phone, baby!
Sure, maybe not as sexy as a Librem 5 (https://puri.sm/products/librem-5/), but who can afford that?
I found the installation process pretty straightforward when I followed the instructions and had an officially supported phone. I omitted the Google apps. Maybe slightly more difficulty than installing Linux on a computer. There's no need to root your phone; it's mainly connecting your phone to a computer over USB and following some step-by-step instructions carefully. The biggest hurdle for me was that the OEM unlocking option was greyed out at first, with a message to connect to the internet or contact my carrier, and was still greyed out when I connected to the internet. At first I was scared my phone was locked, but when I removed the SIM card and rebooted, the OEM unlock option was enabled and I could proceed and unlock the phone.
There were also a few messages that seemed like error messages during the process, but turned out to be harmless. Everything worked in the end.
It's so nice to set up a phone without it asking you to register or login etc. Just a clean, basic phone. So far I've only needed apps from F-Droid for the basic things I use a phone for: calling, email, web browser, alarm, camera, music, podcasts, calendar, contacts, maps, messaging, books, and accessing my files portably.
However, I don't recommend buying a new phone for this purpose. For people who are stuck with a phone that isn't officially supported, or who are less technically inclined and don't want to take the risk / time in flashing a different OS, I made a guide which you can see at https://adam4235.github.io/encyclopedia/computer/android_reduced_tracking.html. That may be almost as good as using LineageOS; if you look at the ways Google tracks you (https://productivityhub.org/2019/05/30/all-the-ways-google-tracks-you-and-how-to-stop-it/), all the things listed there use your Google account. That's if you're concerned about tracking by companies; it probably wouldn't protect you from tracking by governments (the best way to do that is to not have a cell phone).
