Unfortunately, syncing between the iPhone and Outlook at times can be contentious. I experienced some issues with one of the updates before iOS 8.4, and it took a while to recover from. I know that I ran scanpst.exe from Windows on the Outlook.pst file, reset sync in iTunes and a number of other things, so remembering exactly what fixed it is escaping me, but I believe I discussed it with someone else, so I'm trying to find that. It just seems that sometimes working between Windows and Apple can be a problem. If you can, give me a little time to research what I did and I will get back to you.
By the way, where are you located that the Genius Bar will not take appointments except for newly purchased products? I've never heard of that before. Are you trying to make the appointment online, or via telephone? I've never known Apple to deny an appointment no matter what it was. I'd just make the appointment online for an iPhone.