Moon+ Reader is great if you want a library in your phone. It's very customizable, too. But it's not great with PDFs, and few third-party apps are. If you're reading on a phone-sized screen, the official Adobe Acrobat app is the best for text reflow on PDF files. It maintains a lot of the formatting making it very comfortable to read. Unfortunately, nothing else about the app is that great and it won't give you a good library view like you're asking for.