Just chiming in a bit late, the other recommendations of Ubuntu Touch and/or Fairphone + donating are great ideas.

I cant get a Fairphone as they don't work well in the USA, and when the major carriers sunset their 2G/3G might not work at all - I've considered using one on WiFi only but don't know how well that will work yet.

That's also my reservation on buying another device for Ubuntu Touch as well, and VoLTE is device specific - the PinePhone having VoLTE solves that for me.

I'd also recommend to report bugs and the like actively if you have the time, providing good examples helps iron things out for other users and the maintainers.