I've just gone through about 2 or 3 months reading almost exclusively on my phone. I've found that to be more workable than I expected. It limits me to short reading sessions but I only need a small break before starting another session and that turns out to be a good time to ponder what I'm reading.
Starting about 2 weeks ago I've gone back to reading on my ereaders; first my Kobo and now my Paperwhite. I ain't going back to the phone.
Actually that's not totally true. I'll continue to read with the phone when I'm away for short periods because the phone is always with me and it really is a decent way to read. But the ereader, to my mind, is just a nicer and more comfortable way to read, and it's certainly easier on my eyes.
Barry