Deleting Songs from Iphone 4

Ok, I'm sure there's a thread that covers an issue like this somewhere, but everything I've found hasn't solved my issue yet, so hopefully posting this directly will get me some results.

I had a random issue come up when I tried syncing up, and when I tried syncing up a playlist, the songs of that playlist would be duplicated and would run out my phone's memory. Long story short, I couldn't figure out how to keep the songs from duplicating, so I thought I'd start from scratch. I saved all the songs from my library to my computer and then deleted them all from the library. I then tried syncing up my phone to the empty library as a test, but I'll be d----d if all the deleted tracks are still on my phone.

So simple problem, I can't delete anything from my phone. Simple solution, I don't know. Anybody have any ideas?