Android uses a Linux kernel, but most people don’t consider it “Linux”.

A “Linux Phone” is a more traditional Linux distribution made to work on a phone, usually with GNU tools, and a GTK or QT based UI.

"Android is Linux" is a bit oversimplified.

What the is issue, still simply, the way I understand it:

• Linux kernel contains drivers for the specific hardware used in devices (processors, modem, memory, display, camera, etc.)
• Each Android smartphone has different hardware configuration
• Hardware manufacturers want to guard their secrets, so they sign contracts and NDAs with phone manufacturers
• Phone manufacturers create a unique, dead-end fork of a Linux kernel that contains drivers and is configured specifically for that model. (There are exceptions, but generally)

So yes, Android uses a Linux kernel, but in most cases, a very specific one.

Why not replace it? This requires:

• Access to the bootloader and ability to read/write to internal storage on low level, and manufacturers lock it down.
• Knowing the hardware and the drivers. As mentioned, manufacturers will provide drivers only to their contracts. So someone would need to write a driver.
• Once someone writes a driver, it can be added to mainline Linux, available to all.
• That is why "mainlining" a device is a big deal - that means that the kernel for that device can be built, and going forward, that device will be supported for all future kernel versions.

This makes me think how fucked it is that we really only have 2 choices. Android or ios. And Android isn't really getting any better. And it shits me it's owned by Google.

Why Not just fork it

Astronomically easier said than done.

1. Yes, android is technically Linux
2. There are forks (Graphene, e, etc) but none approach the popularity of traditional Android so you’ll never find them on phones sold by major retailers/carriers
3. Theres not a huge market (or rather, it’s not a huge moneymaker) to develop an android fork that focuses on things like privacy and security. There’s a reason phones come preloaded with Facebook and Candy Crush.

Technically most things we call "Linux" aren't even Linux, they're distributions that use Linux as a base. Android forks their own Linux kernel and then shovels on a whole bunch of non-Linuxy stuff on top of it and then locks it all down so that you can't make any changes.
So what people mean when they say they want a true Linux phone is that they want an OS on their phone that behaves more like most Linux distributions (where you are in control, and can even install a different kernel if you wanted).
As for the forking question, being downstream of Android means A) undoing everything they did it lock it down and B) constantly having to do that moving forward as they do everything they can to stymie you at every turn.

It just uses the kernel It doesn't use the traditional desktop user tooling

I'd say on the Hardware side, degoogling is a pain. Android devices are not very 'open'. I think graphene is the only alternative that's easy to install and that only works on a couple of devices. For others like linage there are a few more devices but some of the install procedures are shonky and can leave you with unlocked bootloader and stuff like that. Scares off many people I'd think. I think a device that was designed to allow you to install an OS and is not basically locked down is attractive.

Put another way, you can fork android all you like, but what are you going to run it on, and how do you install it? If there was a device that made it easy , it might get popular enough to attract more interesting open source innovations.

On the software side , once you ditch google there's also way fewer applications. F-droid is ok; but being able to use one of the major distro with an ARM repository would give a decent amount of stuff - albeit not optimised for touchscreen.

I think there's an options also some technical stuff about how much call and cellular data has to go through your cellular network, and whether bypass or switch off is an option - I think that's for the real privacy people - I don't really know about it.

a more technically correct term for the non-android "linux" (minus the kernel) is freedesktop. but "freedesktop phone" would sound somewhat weird

I'd just like to interject for a moment. What you're refering to as Android, is in fact, GNU/Linux, or as I've recently taken to calling it, GNU plus Android 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.

Many computer users run a modified version of the GNU system every day, without realizing it. Through a peculiar turn of events, the version of GNU which is widely used today is often called Linux, and many of its users are not aware that it is basically the GNU system, developed by the GNU Project.

There really is a Linux, and these people are using it, but it is just a part of the system they use. Linux is the kernel: the program in the system that allocates the machine's resources to the other programs that you run. The kernel is an essential part of an operating system, but useless by itself; it can only function in the context of a complete operating system. Linux is normally used in combination with the GNU operating system: the whole system is basically GNU with Linux added, or GNU/Linux. All the so-called Linux distributions are really distributions of GNU/Linux!