Well, over in the Screenshots thread, there was evidence of FreeBSD on a Pine Phone...
Here's FreeBSD 15 running on a Pinephone Pro with a default install of IceWM

No network, no touch input, no USB, so it's pretty much useless at this stage, but hey! I got a legit screenshot

Based on that screenshot, I think that the way things stand right now, FreeBSD on a phone is not a very practical idea. A lot of things don't work right, it probably takes a LOT of effort to just install something, let alone anything useful.
OP would have to be prepared to spend many hours just trying to get FreeBSD to cooperate with the phone. Not even UNIX-y stuff like a functional command line, but more along the lines of embedded programming, knowing what a memory address is, what an interrupt is, knowing why having solid knowledge (of concepts like a stack or a queue or other data structures) is important.
If that is too much, I'd frankly recommend a cheap Lenovo laptop if OP just wants to practice using FreeBSD. Even those can be a nice time sink, but OP will have an easier time getting results out of playing with FreeBSD.
For embedded programming practice, FreeBSD is available for a number of Pi boards on the market. OP should be prepared to spend hours just trying to follow instructions on setting up embedded environments - those things are particularly unforgiving if you don't follow instructions correctly.