I would like to interject for a moment. This statement is technically true but disingenuous and facetious.
While it’s true that Linux is just the kernel, what most people refer to as Linux is actually the Operating System GNU/Linux, or, as RMS would now call it, GNU plus Linux, or sometimes, a less GNU depended, but mostly GNU/Linux compatible OS, or, as I have literally just now come to call it */Linux.
Moreover, a modern */Linux system is expected to be based on SystemD, unless explicitly avoiding it due to some technical constraint or some desired feature of another init system. One could come to call this SystemD/Linux.
And lastly, this kind of use case would be the perfect match for a Wayland shell, as opposed to an X11 shell. Which would be more efficient, and would give the shell more freedom in the management of windows.
As a result, when asking about a Linux phone, we could expect one is talking about a phone running a SystemD+Wayland/Linux OS, or at least a mobile-focused */Linux OS.
The Android kernel is a, largely downstream, fork of the Linux kernel, but the Android OS is in almost no way compatible with any */Linux OS, and it’s instead its own completely different OS.
My sister is an urologist. So for me this is basically what happens opening pictures on the siblings group chat