ADVICE NEEDED! UPDATED

(I'm 16) So nine months ago I messed up and did something to make my parents not trust me anymore. They took away my phone and sold it and I have been grounded from my phone ever since. In those past nine months I have only slipped up once and did something wrong. But now in one month I leave for LA by myself and I want to ask if I could buy myself a new phone. But I don't know how to start the conversation. Help plz.

UPDATE: So I talked to both of my parents giving them all the reasons I should have a phone in LA and they said they would think about it... That's better then what I had before ig💁🏽

Update: I got a phone so thank you for all your advice!