Phone UIs are still screen UIs, but they are not desktop UIs, and that's not because of the shape of the device.
Tell me how that’s not a phone and a desktop:
https://www.instagram.com/reel/DPtvpkSExfA/
That's not a phone and a desktop. I feel like I'm stating the obvious here; it's too big to be a phone, for any reasonable definition of 'phone'.