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Here a couple troubleshooting articles that I would recommend when experiencing issues syncing calendars.
See Pierre-Yves 1 post: https://discussions.apple.com/message/23297197#23297197
This was driving me crazy. Sync between Outlook 2007 and my iphone was working perfectly on ios 6 - I primarily sync Calendar, contacts, and notes.
Then everything went bizerk with ios 7... All of a sudden nothing was getting syncronized, but rather multiple Calendars and Contacts showed up in Outlook 2007. Disabling Calendar, contacts, and Notes in my iphone's icloud settings did the trick. Now I have ONE Calendar and ONE contact list in Outlook, fully in sync with my iphone.