I think you may get dry eye and itching eyes from reading too much on iphone. But as to watery eye, you may get a cold or an infection, because my grandma often has watery eyes when she gets a cold. You can use some artificial tears to relieve your symptoms and do not rub your eyes, because rubbing your itching eyes may cause red eyes or infections.
Dear friend, if you don't know what caused your itching and watery eyes, you can consult your eye doctor and have your eyes examined. But I think your symptoms might be caused by your long time of reading on iphone. I suggest you to take a break every half an hour and look at the distance for a while.