(But yes. The screen thing is the main issue for me. I would actually consider a decent e-reader better if they were bigger than a phone screen.)
Karn, most (all probably) ereaders have screens considerably bigger than phones. They are typically about the same size as a paperback with a 5" to 6" screen.
Oh and if, as you suggest and like me, you haven't got the best eyesight then the ability to bump up the font is just wonderful. More page turning but less eyestrain; that's actually a benefit I hadn't anticipated but is now one of the main pros for me.