Why isn't iPhone syncing Calendar items with Outlook?

The best troubleshooting I have found for this problem is iPhone, iPad, iPod touch: Troubleshooting contact and calendar syncing via USB on Windows(Apple), mainly due to the fact that it explains how to reset sync history in iTunes, a process that reevaluates the contents of both devices and tries to resync them.

Another good little trick is to try a "Replace data on this iPhone" near the bottom of the info tab, that will wipe the specific data set off the iPhone and replace it with the computers, often a good way to get them talking to each other again.

http://www.sync-iphone.com/contacts-calendars-email/sync-iphone-with-outlook.html#sync-iphone-with-outlook-two-way

• This is unfortunately a one-way synchronization from Outlook to iPhone. To sync iPhone with Outlook two-way, use Google Calendar Sync and select 2-way as the Sync option
• This procedure works for both Mac and PC
• Your calendars must be Outlook 2003 or above compatible
• Once you complete the above procedure, your iPhone Contacts will synchronize every time you connect your iPhone to your Computer
• In case of any iPhone Contacts synchronization problems, on your iPhone go to Settings->Safari->Clear Cookies and restart the Contacts application (if your iPhone supports multi-tasking, make sure you have actually closed the Contacts app)

If this isn't what you want, then you need to sync with an Exchange server, then you can do it in almost real time over the air.