Whenever I want to study, I think about stopping playing with my mobile phone after 10 minutes of playing, but I always procrastinate, and then I play with my mobile phone until I go to sleep, without the energy to complete the task of the day, and then postpone it until the next day... 
The first thing I would do is uninstall all the unnecessary apps. It is very hard to stop gaming when we constantly see the Apps and just can click on them. If this doesn't help you much and you will just go and reinstall the Apps, I would recommend you give your phone to your parents or girlfriend for 1-2 hours and only get it back when you finish your tasks.