How can I check if my phone is payed off?

Hello,

There are a few ways an iPhone could be purchased using a payment plan such as Apple Card, a cellular carrier, or traditional lending. To discover if you have paid off the Toal balance due you would need to check with the lending provider. The below link only apples if you used the Apple Card Monthly Installments.

How to view and pay Apple Card Monthly Installments - Apple Support

"View Apple Card Monthly Installments

1. Open the Wallet app and tap Apple Card.
2. Tap the More button , then tap Monthly Installments.
3. If you have multiple monthly installment plans, tap the one that you want to see.

To see more details, tap Total Financed. You can also view Apple Card Monthly Installments online.

When you buy an eligible Apple product by choosing Apple Card Monthly Installments as your payment method, you'll get a 0% APR installment.1 After your installment purchase, you'll get a notification on the device that you use to manage your Apple Card Monthly Installment. You can tap the notification and unlock your device to see your monthly installment details.

If you use your Apple Card to pay for a purchase all at once, instead of over time, your purchase will be subject to your standard purchase APR.2"

I hope this helps.