Please provide a more sophisticated description of the issue. In particular, include a crash log.

Perfect!

Ah. The .x in the version number means that it is supposed to work on all subversions of 1.18. This is of course a bit speculative on future code changes, but usually works fine for Phosphor. So, unless stated otherwise, it can be expected to work.
Curseforge and Modrinth only allow to set individual versions, though, and I have now updated them.

Phosphor 0.8.1 is not published on Modrinth. This made me think that it didn't yet support 1.18. I have little-to-no knowledge when to comes to publishing mods, but I believe this (should) be an easy fix.