Hello.

Having an average  knowledge  on 11th syllabus may be sufficient  enough  to get you clear an exam, but it may not be sufficient enough for scoring a good rank.

I advice  you to study harder and solve and practice more questions. 

I suggest  you to fix a time table, possibly  with breaks, for you to refresh  your mind. If you are addicted  to your phone, I would  recommend  you to switch on your phone off during studying and strictly stick to your time table, and switch it on only during your break.

You may gradually  increase  your study duration  and you will soon loose your addiction  over the phone.

Hello dear ,
Yes of course you can get a good rank in jee but there's a condition for this . The condition is need to be determinate and need to work hard.
Coming to your mobile addiction, you can use it as boon , now there are number of youtube channels where teachers teaches you syllabus of jee , subscribe those channel and sit to watch the videos with a copy and a pen so that you can parallely note important points.
Make a routine and follow it .
Apart from covering theory , devote minimum of 2.5 to 3 hours to solving only numericals.
thankyou
Feel free to ask your further queries if any.