I deeply want the equivalent of Debian on a phone.

Rock solid. Every few year feature updates, only security fixes otherwise.

You can install debian on a pinephone https://wiki.debian.org/InstallingDebianOn/PINE64/PinePhone

But for a "normal" linux environment on a phone I recommend postmarketOS. They make an effort to support a variety of user interfaces, init systems, devices.

Still, it is important to consider that the hardware and driver support is the limiting factor here. The camera is very bad on the pinephone because it doesn't have the image processing capability to record video in realtime. It also has no OpenGLES3 or Vulkan. Very poor lima GPU.

Plasma Mobile[0] on Mobian[1] is getting pretty decent.

[0] https://plasma-mobile.org/

[1] https://mobian-project.org/