Iphone calender not syncing onto Ical

I looked back a few posts but didn't see this problem listed...

The events I sync to the phone from iCal appear on my phone just fine but events I write in on my phone don't transfer over to iCal anymore. It used to sync both ways just fine but since I did the latest iPhone update (iphone 3g btw) it seems to have stopped working.

Any ideas on how to fix?