There are a bunch. I tried Jerboa and then Voyager on android. Jerboa is the official one, I found Voyager to be a bit nicer, but in the end I find it better to use a browser including on my phone. I sometimes think of writing my own client to reorganize the UI to be more like a usenet client, or maybe even just write a Lemmy to NNTP gateway. I don't understand why it wasn't done that way in the first place.