A phone is a special purpose computer.

For it to be general, I should be allowed to do everything I can do with a PC, without any kind of constraints or workarounds.

Exactly because most people pay more than $300 for an unconstrained device, there is little value to pay more than that for a constrained device.

Are you talking about a "dumb" phone? That I would agree is a special purpose computer.

A smartphone is definitely a general purpose computer, though. The definition of a general purpose computer isn't "a computer that can do anything a typical PC can".

A proper definition would be something like "Any computer-based device that accepts different applications". It's a differentiator between things like microwaves, which are technically computers, and smartphones/laptops/PCs/tablets.

So how do I run Android Studio on my general purpose phone, without workarounds like connecting to a VM in the cloud, while looking at an usable screen?

Mobile OSes are special purpose, constrained to their phone + apps, developed by on external devices.

You don't run Android Studio on your phone. Being able to run Android Studio isn't the definition of a general purpose computer.

Being able to develop software for a device on that device also isn't the definition of a general purpose computer.

A general purpose computer is one that can be easily made to run different programs. Again, it's a differentiation between devices like microwaves and ovens that are technically computers, but aren't used like computers by the general public.

So my car, TV and fridge use general purpose conputers from your point of view, thanks Android Car, Android TV and Android Things.

I guess I will prepare that accounting document with a Bluetooth keyboard paired with my fridge.

Most people don't pay more than $300 for their phone. The average selling price for Android phones worldwide is around $230. In the US it may be higher because all of the major carriers offer payment plans.