Maybe save your money, allowance or get odd jobs around the neighborhood walking dogs, babysitting, mowing lawns. Once you have some money saved...like 1/2 the cost if the phone, then approach your parents and ask if they would help you buy the phone, and show them how responsible you've been in trying to save the money yourself.
You can't depend on your parents to buy you everything. Maybe won't buy one for you but they will probably will let you get one if you save up your money and pay for one your self.
Maybe look for a job and start making your own money.
Ask for an early birthday or Christmas OR promise to find a job to help pay for the phone and subscription.