I'd just like to interject for a moment. What you're refering to as Linux, is in fact, GNU/Linux, or as I've recently taken to calling it, GNU plus Linux. Linux is not an operating system unto itself, but rather another free component of a fully functioning GNU system made useful by the GNU corelibs, shell utilities and vital system components comprising a full OS as defined by POSIX.
While people know that Android is based on Linux, a fact that isn't in question, when people say a "Linux" phone, they're not discounting that Android exists or that it runs Linux, they mean to infer that they're discussing non-Android Linux phones. If they meant Android as a Linux phone, they would have said Android.
While android is in the set of "Linux", not all things that are in the set of Linux are Android.
Since we have a specific word for GNU/Linux - Android devices, but almost all Linux based alternatives to Android for mobile devices is basically referred to simply as a "Linux phone", it can be, and should be, assumed that the speaker is referring to Linux phones which are not Android.
It's a nuance of language and technically not wrong to say that "Android is Linux" but that's not what most of the readers understood to be the speakers intention.
That was the correction that the previous poster tried to portray.
Simply put, most Linux enthusiasts and community, doesn't really consider android to be "one of them" since, though it's Linux at its core/kernel, almost everything built on top of it from there is some bastardized/closed source software, or relies on something closed source. Most of the things people want to run on their phone (browsers, camera software, even the dialer), is almost entirely written, controlled and closed source by Google. While some of the "guts" of the OS might be open source/GNU versions, the interfaces are largely all closed source software that Google has published to run on top of Android specifically. This doesn't fit with the philosophy of GNU/Linux, and therefore Android is largely not included when speaking about Linux, at least for Linux enthusiasts.
No you're using Termux with bash. Unless you're actually interfacing with the kernel directly in which case ignore me and carry on.
Anyways this is a great example of why "Linux" as the name of the OS is stupid. GNU/Linux is better (for GNU-based, obviously, don't go wheeling out the Alpine copypasta because I'm not talking about that).
Alpine Linux is actually a great example of why you are right. Because when people say Linux to describe the OS, they almost always mean GNU/Linux (Linux Mint, Arch Linux, etc). But then there is Alpine, which also calls itself Linux, but its developers actually mean something very different, because it's not GNU/Linux. So that only makes things even more confusing. Android doesn't even use the mainline Linux kernel, so calling it Linux is probably even worse than with Alpine.
If we always used the correct names, there wouldn't be so much confusion.
I think they use some very old and heavily modified version of the Linux kernel, so it's not the same Linux kernel we use on desktop. Then each phone manufacturer adds custom patches on top to support their hardware. GNU/Linux phones also require a custom kernel, but the community is working on upstreaming those patches, so that they can run mainline kernel some day (PinePhone Pro and Librem 5 probably already can now, but some stuff might not work).
Yeah, using the name Linux for both the kernel and the operating system makes no sense and it's super confusing. When people say Linux when talking about the operating system, they almost always mean GNU/Linux (like Linux Mint, Arch Linux, etc). But then there is Alpine Linux, which isn't GNU/Linux and that makes things even more confusing. If I didn't know what Alpine Linux or Arch Linux was (and had no knowledge of distro names), based on their name I would assume they are some kind of fork of the Linux kernel. Arch Linux should have really been called Arch GNU/Linux and Alpine Linux should have just been called Alpine OS.
They use the current LTS kernel that exists when the phone exists. If your phone has an outdated kernel (mine had one too, and I thought the same) it is simply really outdated.
Yeah the problem lies in the many Distros I think. The BSDs are all different bundles, not like Linux+Gnu+Systemd+pipewire+wayland+glibc and some minor differences. FreeBSD is actually different from OpenBSD for example. Then Android is also a single project, just like this "modern desktop linux bundle".