I’m upgrading my iPhone and trading in the old one. I had to erase the old one completely and unhook “Find my iPhone” from it.
I’d seen headlines hinting that recycled iPhones aren’t often erased. Some headlines suggest that the erasing operation itself doesn’t really work.
It works. It’s just time consuming. I turned off TouchID and the lock code. I disabled “Find my iPhone” and all the iCloud connections. Then I went on line and made sure the old phone wasn’t listed on my Apple account. Finally, I hit the “Erase All Contents and Settings” option.
The phone restarted with the Hello setup screen. I went through guided setup without hooking up iCloud or anything personal. I looked through the phone to make sure nothing was there. It was clean. I looked on Find My iPhone, and the old phone didn’t appear.