To stop paying for an app subscription on your iPhone, you need to cancel the subscription through your Apple ID settings or the App Store. Here are the steps:

1. Open the Settings app on your iPhone.
2. Tap your name at the top to access your Apple ID settings.
3. Tap Subscriptions.
4. You will see a list of your active and expired subscriptions. Tap the subscription you want to cancel.
5. Tap Cancel Subscription at the bottom.
6. Confirm the cancellation when prompted.

Alternatively, you can cancel subscriptions via the App Store:

1. Open the App Store app.
2. Tap your profile icon in the upper right corner.
3. Tap Subscriptions.
4. Select the subscription you want to cancel.
5. Tap Cancel Subscription and confirm.

After canceling, you will still have access to the subscription features until the end of the current billing period, but you will not be charged again

. If the subscription was not purchased through Apple, you may need to cancel it directly through the app provider's website or customer service