Would running a Lemmy/kbin instance on your phone be feasible?
Libp2p or similar stack could be used to provide the phone instance an address, caching could be distributed among peers. Of course, as long as other servers also support libp2p.
I dunno. If you could run some distro like mobian on some phone with an 8 core processor, could be a decent choice for a little instance.
I think you'd want to use a phone with USB C then use a powered USB-C dock with wired ethernet, but get to square 0 and I bet you'd have something that could really sit there just serving for a long time. I'd be a little concerned with IO access since the internal MMC would be constantly hammered, but there are USB-C external drive enclosures you could easily use that for storage and not have to worry about mutilating your phone's mmc.
Part of me wants to try sometime just to prove it can be done.