I meant a desktop, obviously. I use an iPhone and I'm fully aware it runs macOS with a different desktop environment. All Apple devices run macOS, but the interface will be adapted to fit the hardware. It's all macOS underneath though, which is UNIX.

It's easier to explain Android, especially to anyone who knows Linux. So Linux isn't an OS, it's a kernel. The OS (or distribution, or "distro") is a collection of software bundled with the kernel that operates a computer. Android is a Linux distro for phones. Plug one into a TV and see what happens (ideally a Samsung). Apple could do this too, have your iPhone or iPad go full macOS if you put it on a big screen, especially if you also connect a keyboard and mouse. It's just a matter of including that desktop environment... and maybe a couple other things. But Android already does it. And it's awesome. So yes, they're computers.