It can be as simple as just putting an app on your phone. I use feeder which is fine. Pretty bare bones, but in that way it's easy to learn and use.
I've also been meaning to try out an app called Nunti, which I heard about a while ago from this Lemmy post. It claims to be an RSS reader with the added benefit of an (open source and fully local) algorithm to provide some light curation of your feed. It looks interesting, but I haven't actually tried it out yet because I'm still deciding whether I want any algorithm curating my feed, even one as transparent as Nunti's. It's also only available through F-Droid right now, which is a bit of a barrier to entry.