Yes, it is very bad for eyes. I don't know what feel you have, I feel my vision blurred, eyes sore and red after reading on my cell phone for hours. One of my friend complained about this too. She once got her eyes injured by accident. Recently she always told me her vision was very blurred especially after reading on phone in bed. It is very easy to understand why this could make eyes uncomfortable. With smart mobile phone, we could read, play games and surfing on internet wherever and whenever we want to. However it also means we are looking at this small screen for very long time with unstable light and bad posture. We also know that dim light, pro-long working time and bad posture could make it easily to get eye strain. There are some symptoms you might develop, for example redness, dryness, grittiness and blurred vision. Even headache might be caused by eye strain. So I suggest you not to reply totally on mobile phone. Take more exercises. Have frequent sight focus break. Doing some eye exercise would be great for your eyes.