You seems to have symptoms of computer vision syndrome and dry eye. Let me put it this way. When you use a smartphone, the muscles in your eyes contract to focus on the screen and stay contracted for the whole duration of smartphone use. This puts enormous strain or your eyes if you continue using the phone continuously without taking properly timed breaks in between. Its something like (and this is just to give you an idea) going to a gym, lifting a pair of very heavy dumbells with outstretched arms and staying in that position for a very very long time. Those muscles will definitely get tired.
So, now with those tired muscles when you try to focus on other near objects, they will not be able to function properly and you will have difficulty focusing.
Next Steps
No, you dont need to stop using your phone completely. You just have to take breaks for a 20-30 seconds every 20 minutes. Try to blink more when you are using your phone, Use lubricating eye drops, get your refractive status checked after consulting an ophthalmologist.