To the phone folks, since it seems like people these days are too lazy to try figure out things on their own.
Firstly, idk if it works on iPhones, I don't use them since they are so limiting.
If you use an android – get firefox mobile (or anything that supports extensions like Violentmonkey on mobile), download said extension and then get yourself either: 4chant XT (for some reason it works better on mobile than 4chan X, at least in my experience). It is a bit clunky on mobile though, but works well for soundposts.
Alternatively get 4chan Gallery, as it doesn't change the whole fucking website it's less annoying on mobile, however, it is a bit retarded when it comes to loading soundposts and it can take a second to load; you sometimes need to reopan the gallery. It also requires you to edit a bit of its code to function properly on mobile (grid display doesn't really work well on phones). It's a very easy edit, but the editor is not the most cooperative sometimes (common phone L).
Here is the bare minimum of the code editing you have to do for the gallery to be somewhat functional, preferably you should edit more so it is more convenient to use, but if your goal is just to hear soundposts it works.
Turn off auto-updates of the script so you don't have to edit it again.
If you choose to settle for 4chan Gallery just keep the XT downloaded, but turned off. Sometimes it just doesn't want to cooperate and quickly turning XT on/off is less of a hindrance.
