What is "mainline Linux"? The current kernel?
When a phone is "mainline Linux compatible", what does that entail? That the kernel can be made to boot? That the kernel can access all the hardware?
That there's a full graphical UI that can also access all the hardware?
And what is an "Open source OS compatible phone"? A phone that can run an open source OS? AOSP is open source. Does that mean all Android devices then? Are we allowed to add firmware blobs? LineageOS does exactly that. Again, that would add a huge pile of devices nobody's interested in listing here.
I could go on for hours.
This is a pet peeve of mine.