Resync iphone photos to macbook Photos

I'm trying to save ALL of the photos from my iPhone 5 (almost 2000 of them) to my macbook pro.

However, when I plug it in with a USB, only about a half of the photos show up on the Photos app. I can't see any logics as to which ones are missing, it seems to be totally random. I've tried changing all possible iCloud settings on the iPhone as well as the macbook which only resulted in some photos being present in my library twice or even three times. Long story short, the sync is totally messed up.

Hence the question: is there a way to "reset" the sync between my iPhone and the macbook? I'd like to empty my library on the macbook completely and then sync the iPhone again in the hope that this time all the photos from it will be synced.