If you need to erase data from your iPhone, then there is a very straightforward process to ensure that your privacy and personal information is protected.
First of all, you need to open the settings app on your iPhone. After that, you will need to scroll down to General. Once on General choose the Transfer or Reset iPhone and this will take you to two options, including Erase All Content and Settings.
Make sure that before continuing you have backed up all important data on iCloud or another device to help your data from being lost. When you click on Erase All Content and Settings, it will erase all the data of your phone, including videos, photos, apps, contacts etc. Another precaution is logging out of iTunes or iCloud to ensure that no data of yours is backed up.
Lastly, remember to remove any external storage devices and your SIM card. After following these steps you can ensure that all you personal data is protected and safe.
Further reading
Android file recovery
Recovering lost iPhone data with no backup
Deleting a file does not delete it