Hi and welcome to the forums. Are you saying your appointments are duplicating? I guess my question would be are you also syncing your calendars between the devices (so your exchange appointments show up on your google calendar?). If so, I think they will duplicate on the phone as well (since it doesn't know they're the same appointment)
You can go into your phone's account settings (menu - accounts) and click on each account and tell it whether to sync the calendar or not. For example, I only sync my google and exchange calendars (and that's it), but they just merge together on the phone, but don't duplicate.