How do I permanently delete an app from my iPhone?

On an iPhone with iOS 14, if the app is on a Home screen, touch and hold the app, tap Remove app and then tap Delete App (or tap Edit Home Screen in the pop up menu, tap the minus sign, then tap Delete App)

If the app is only in the App Library screen (swipe left past the last Home screen), touch and hold the app there and then tap Delete app.

Note that some built-in Apple apps cannot be deleted.

If neither of those options is available, there may be a restriction set on deleting apps. On an iPhone or iPad, go to Settings > Screen Time > Content & Privacy Restrictions > iTunes & App Store Purchases > Deleting Apps.

See: https://support.apple.com/en-us/HT201304#prevent-purchases

Be aware that deleting an app does not cancel any subscription related to that app. To cancel, see: How to cancel a subscription from Apple - Apple Support