A blog post by https://kopiti.am/@nondescryptid detailing how they set up postmarketOS on their own phone:

I’ve got a Samsung Galaxy S II (i9100) lying around, and decided to try seeing if I can repurpose it and get it to host a blog. I was inspired by compost.party – a very cool server running off a Xiaomi Poco F1 using postmarketOS and a solar panel for charging.
The physical nature of computing is usually not a concern, as things are sufficiently abstracted for me to not have to care too much about it. But trying to revive this phone from 2011 was a reminder that when we talk about compute, we are ultimately dealing with physical resources – tiny towns with blocks of silicon, lithium, etc etc.