Hi mom, I think I can handle the problems you mentioned properly. Here are some plans to make sure the things you worry about won't happen:
1. You can take me to do eye exams every month to make sure my eyes are not getting bad. If my eye-sight becomes worse than the current situation, I can return the cellphone to you.
2. You can set the phone to limit my screen time to one hour per day, so that it would not take my time to do other things.
3. You can set the phone to limit my screen time to one hour per day, so that it would not change my habit to use my attention too much. Also, I will keep reading books and discuss my thoughts with you, so that I can practice deep thinking skills.
4. I can start by having a cheaper phone and I will take good care of it. If I don't lose or break it for half a year, you can trust me and buy me a better one.
Does it sounds good to you?