@MikeWardPT There are two things, the one are installments for the phone, there other is the remaining amount for the subscription. I assume he got the cell phone for a reduced price because he took out a subscription, regardless of whether he paid it off in installments or not. This means that the remaining amount for the phone and the remaining amount for the subscription must be paid by the end of the minimum term.
Example: The subscription has been running for 6 months, to cancel the subscription now, you still have to pay the subscription costs for the next 6 months to end the contract now, i.e. 6 times the monthly subscription costs.
In this case, plus the costs for the remaining unpaid installments for the phone. Installments and subscription are linked.
Personal tip to everyone reading here: Never, I repeat never, take out a subscription with or without installment payments for a device on your account for a person outside the household//close family members. In the word case scenario, you will be stuck with the costs yourself.