You could try resetting your sync history as described here: http://support.apple.com/kb/HT1692. Doing so will trigger a merge or replace prompt for calendars and contacts on your next sync to be sure to follow the guide carefully to avoid creating duplicates. (If you choose the option to delete the data from Outlook prior to syncing, be sure to first back it up in case something goes wrong. Also, the guide should say for this option that after deleting you data from Outlook you must go back and enter at least one contact and one calendar event in Outlook prior to clicking Apply, then when prompted, choose Merge. If you don't you will lose your contacts and calendar on your phone as well.)
I just figured out why my iphone 4s stopped synching via icloud with my Outlook 2010, and wanted to pass on what I found in case you do not yet have a solution. I discovered that in my iphone settings/mail,contacts,calendars the default calendar was now set to the "On my phone calendar" instead of my "iCloud" calendar so all appointments I made were going into a local calendar and did not show up in Outlook. I don't remember making this change, but I suppose I might have, perhaps it occurred in an update? Hope this post will help you.