From what you say iTunes thinks you are syncing via iCloud over the air.
For that to work would require you to have your iCloud account set up in iCal > Preferences > Accounts to let iCal see the iCloud calendars. You would also need to have the iPhone set up to sync to the iCloud account.
If you want to sync via iTunes I would look on the computer's System Preferences and see if you have iCloud set up there and if so remove it.
Information for troubleshooting iCloud syncing: http://support.apple.com/kb/ts3999
Apple advises against syncing both with iTunes and iCloud because you will end up with duplicate events.