A phone? Really? I don't even know how to hack stuff on my phone and I'm a professional programmer. Nothing wrong with a PC, it's just much bigger, more expensive (although second hand gear is probably cheaper than this, it just won't look as good) and a much bigger barrier to entry as most people don't know how to install Linux on a PC. The Raspberry Pi is literally "do this to the SD card then switch it on". Plus it has GPIO pins and ready to use Python libraries for them. It's literally made for learning.
Phones are not designed for content creation (and more broadly, treat on-device development as a second-class activity at best), while PCs are much more expensive and you could damage the Windows install by installing Linux in dual-boot.
By comparison, a basic Pi is development friendly, easily fixable, fairly cheap and inexpensive to replace if broken. If you already have the peripherals, the cost is quite low.
Also, is everyone missing that this is about the Raspberry Pi 400. Why are half the comments about Raspis in general and running servers on them etc?