in my opinion i think you should get a job and buy the phone with your money so if you loose it or its stolen your parents wont bother you because you bought it with your money.thas what i did i bought my phone with my money because i sell the phones sometimes to buy new ones and my parents don't say anything to me because i bought the phone.
Tell him you'll need it for emergencies or meeting your parents after school
or just ask around bday/christmas.
Try and pay for part of it too.
Hope I helped and good luck!