I took the headphone socket out of an old radio, soldered it to stripboard, stuck on a header. Did continuity tests because I am very bad at soldering. Burnt my finger. But now I have serial access to my new pinephone so that I can break it in new and unusual ways.

Update. I soldered a few pins to a ttgo/esp32 board, and using the fabgl terminal sketch was able to get an ssh connection to a remote box, using ps2 keyboard and vga output. No desktop needed.

It is not exactly perfect, but I think this may be due to the terminal software on the esp being more proof of concept than production ready.