Setting up iCloud Photo

I don’t know if the iCloud setting is called “Download Originals” or “Download and Keep Originals” - I’ve seen both names in various articles - but I’m confused about one thing...

If I turn on iCloud Photos and choose the Download (and Keep?) Originals option, does that mean all my photos will disappear from my phone and go to iCloud, and then I have to individually download them back into my iPhone? Or will the original photos remain on my phone but also upload to iCloud?