Jerboa if you're on Android but it has a login issue that makes it unable to connect to instances that are still running the 0.17.4 version of the backend (and among them is lemmy.world). You'd have to wait for those instances to update to the 0.18.1 when it comes out before you can use Jerboa reliably.
Meanwhile, you can just open the web UI in your mobile browser and it will work just fine.