Thank you for writing, You are smart to catch this habit now. Actually, I think that it could be that you don’t think you are as smart as you really are. Often teens (and adults for that matter) who don’t have enough self-confidence leave things to the last minute. That way, if something isn’t as good as it should be, they can always tell themselves “Well, if I had given it more time, it would have been perfect.” By never giving things enough time, they avoid having to face that just maybe, even if they tried their best and given it plenty of time, the project wouldn’t have been terrific. Of course, it also means that they never find out that they did fine. Think about whether this applies to you. If so, the only way to combat it is to take a deep breath and give yourself the time you need to do your work and see what happens. Chances are you’ll do a fine job most of the time. When you don’t, you’ll find out what you need to do to improve the next time.
As for being on your phone: This, I’m afraid, is a problem that is becoming more and more common — by teens and by adults. The “clickbait” on phones and people’s worry that they may be missing something keeps people on their phones too often and too much. The way to deal with it is to put yourself on a “phone diet”, at least when you have homework to do. Ask a parent to hold your phone until you can show them that you’ve done your work. Yes, you will probably suffer some “withdrawal” at first. It might help if you tell yourself that the quicker you get your homework done, the quicker you’ll get your phone back. Give it a try.
I wish you well.