Because I don't own a kindle nor am I willing to use their app. I'm either old and stubborn or principled, but I want to use my current phone and "system" I've

Because I don't own a kindle nor am I willing to use their app. I'm either old and stubborn or principled, but I want to use my current phone and "system" I've been using to read ebooks for the last 15 years. (It's possible that kindle unlimited is a cheap enough system to make dealing with amazon software, but amazon is annoying enough that so far nothing has convinced me to buy into it)