I'm selling my iPhone. How do I make sure my private photos are really gone?

Modern iPhones encrypt storage, so Erase All Content and Settings destroys the key and makes old data unrecoverable within seconds. The risks are mostly in what's left around the phone.

Checklist

1. Back up the phone, and confirm your vault's encrypted backup is up to date.
2. Sign out of iCloud: Settings → [your name] → Sign Out. This also turns off Find My.
3. Settings → General → Transfer or Reset iPhone → Erase All Content and Settings.
4. Remove the SIM or delete the eSIM.
5. On another device, remove the old iPhone from your Apple account's device list.

Don't forget

Shared albums you created, photos you've sent in messages, and other devices still synced to iCloud Photos aren't affected by erasing one phone.