If I reset my phone, will I lose everything?

So I'm selling my iPhone and before I do that I want to make sure everything on my phone is completely gone. If I click "erase all content and settings" will it really delete EVERYTHING on my iPhone?

Yes you will loose everything; hence "Erase ALL content and Settings".

When you do that, iOS will erase everything you downloaded/added and replace everything with default values/options.

Yes…