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?

IPhone 5c screen broken but device is recognised by my computer

After my iPhone 5c dropped, my screen no longer turned on; moreover, the screen is not cracked.

When I plug my phone into my laptop, my laptop recognises it, however, to allow access to my photos/videos (that I haven't backed up), I need the screen to work. - I need these photos.

After calling Apple Care, they told me to wait some hours and see if my screen turns on, otherwise I have to go in for a factory reset and everything will be lost.