you can get phones that allow AOSP. Most xiaomi phones do. I have one running exclusively FOSS apps.
If you don't mind the form factor, the Pyra is coming out this year
Although I still don't think it'll make for a very good phone, and I say this as a backer that's quite excited to get his hands on the Pyra. I'd look towards the Librem 5 for a more realistic phone experience.