How to get rid of greyed out songs on iPhone?

I deleted a bunch of songs from my iPhone 4 (on the iPhone) and today I connected it to iTunes and synced (I believe thats all i did) my phone to it. So I disconnected it and now all the songs that I deleted are showing in my Library except they're all greyed out and I can't listen to them, tap on them, or get rid of them. The songs are only on the phone so is there a way I can get rid of them that way? Why could I have done on iTunes that caused this?

"is there a way I can get rid of them that way?"

Connect to iTunes, hit CTR: S

Enable manual management on the summary page.

Click on the iPod music tab.

Highlight the grey files and erase.

"Why could I have done on iTunes that caused this?"

It's possible that your iTunes software was recently updated, but you haven;t yet restarted your computer.

Try also a full shutdown and restart of the iPod.

Lastly, don;t sync - use manual management. It's an altermnative to syncing but is still part of iTunes. Most people use sync because it's a word that many non-tech savvy people can use w/o understanding. It means whatever they want it to mean. It also causes many headaches that I've never had in 3 years of using my iPod Touch.