How to securely erase an iPhone in just 3 steps
There are two main scenarios in which erasing an iPhone is called for: Either you’re getting a new phone, or the one you have is having problems.
The most common reason involves iPhone owners who trade up to newer models, usually in the fall after Apple unveils its latest line-up. Let's say you buy the new iPhone X and then plan to trade in or sell your older iPhone 7; you’ll need to make sure your data is no longer present once the old phone leaves your possession.