While trying to delete data off iPhone 4s?

The lock button on my iPhone 4s (that I've had for less than a year) broke, so I went to the Apple store to get it fixed. They said I could get a new iPhone for free, which is great. But, they couldn't give it to me yet because not all of my info was backed up on iCloud. Evidently, I didn't have enough space to back it up.
The nice worker told me to delete at least 4 GB of pictures (I had 10 GB worth of pics.whoops) so I did that. I deleted over 2, 000 pics off my phone and kept them on my iPhoto, which gave me a lot more storage room.
BUT, now I'm trying to sync my phone normally and it says on my iTunes, "Adding 1, 750 pictures to iPhone… "! Because now I think my computer is trying to add all these pics to my photo library on my phone. The GB just keep rising now, thanks to my computer trying to re-sync the photos.ugh.
Sorry if this is confusing, I'm not the best with technology but I usually know what to do.
Do I just never let my phone sync the pictures with my computer?

Ok you don't even need to back up to iCloud instead back up to your cOmputer where you have much more available space. There's a setting where you can choose to back up to computer when plugged into iTunes. As for the pictures, when plugged into iTunes clock your iPhone on the left and then click the navigation button for pictures( next to music, apps videos etc in the middle of the screen when iPhone is connected. There should. E a check Mark that you uncheck to de select it.