Originally Posted on March 3rd, 2023.
There is a third OS alternative to phones now; Linux.
Like on computers, there are multiple different distributions of Linux OSes available; Ubuntu Touch, Sailfish, Pure or Manjaro for example.
I’m going to present a few Linux phones here that you can research further for yourself.
Sony Xperia 10 III with Sailfish OS

I am very curious to try one of these phones. With a license purchased from Jolla, you can even install android apps. You can either buy one of these phones from a reseller and flash it yourself, or you can purchase a used phone from jolla with Sailfish X pre-installed.
Note: These are the phones that currently supports Sailfish X:
Sony Xperia™ 10 III, Xperia 10 II, Xperia 10 and 10 Plus, Xperia XA2, XA2 Plus and XA2 Ultra, and Xperia X.
If you have any of those phones already, you can try out Sailfish OS for free. Note that the free version doesn't include android app support.
Volla 22 with Ubuntu Touch, Sailfish OS and more
The Volla 22 comes with multi-boot function, making it possible to install Ubuntu Touch, Sailfish OS, Droidian or Manjaro. Perhaps even more in the future.
I'm not sure about the Android app support on these platforms. I do have the original Volla Phone with Ubuntu Touch on it, which doesn't run android apps at the moment. One day I will try to install something like Waydroid on it, and blog about my experience.
Pinephone or Pinephone Pro

Link: https://www.pine64.org/pinephonepro/
The pinephone is a relative cheap phone good for testing and development. It comes shipped with Manjaro but it supports virtually every Linux OS that can be installed on a phone today.
I don't have one myself, but at a glance:
It seems like it's not the best hardware, but the price for the Pinephone reflects that.
Not the most user friendly phone. They even admit that on their website.
Very flexible phone in the sense that you can install any Linux OS you like
Hardware switches for GPS and WiFi assures you that those functions really are turned off, not just in software.
Conclusion
This phone is cheap, good for testing and developing, privacy oriented but is not for regular consumers. With some work, it could probably become a good cheap alternative for regular consumers, but it's not there yet.