I definitely want an open-source phone for all the reasons you mentioned, but I absolutely also want a Linux phone.

I'd love to live in a world where BSD or Minix became The Thing™, but since it didn't I basically live and breath Linux for work and that spills over into my personal usage too. Interoperability between my phone and my laptop is huge. I recently started using KDE Connect (and okay - that doesn't have to be Linux-specific) and being able to seamlessly copy / paste between devices, etc. is a game changer for me.