iPhone sync/backUp

Hi and thanks in advance for your help
forgive me for my basic terminology..I'm NOT a tech guy at all

need to clean up for space on my mac but can't find what took up 16G of space during a screwed up sync I performed with my iPhone

iPhone has 28G taken with lots of video

1. started a sync/backUp of iPhone to my mac
2. during the sync I opened the 'get info' window and watched the 20G left on my mac going down fast, I knew that it would just jam and not complete a proper upload, so I stopped it and unplugged the iphone from the mac so I can free space on mac to handle a large upload from my iPhone
3. my mac internal HD is now down to 4G but I can't find anything on my mac that came from my iphone?
4. looked in internal HD library for mobileSync/backup but it's not there...
5.also in iTunes and iPhoto on the mac - i don't seem to have been uploaded from my iPhone
6. so now I have a computer with no space left and an iPhone with no space left ... don't know what to do

 

thanks so much
got Disk Inventory X
was very helpful
peace