I am, indeed, saying exactly that: unless one has Microsoft Exchange (which I don't), one can only sync Outlook calendar and contacts with the iPhone by way of iTunes. If you still doubt, google it. (There may be someway to do this through Google/cloud, but I am not interested in doing it through the cloud). This IS an iTunes sync issue and it is an issue of iTunes losing any/all knowledge of the iPhone, despite both being on the same network. It so happens that Outlook is sync'ed through iTunes, also, in addition to all the other things that one syncs through iTunes. In the Settings list, on the left side of the iTunes page, the choices are: Summary, Apps, Music, Movies, TV Shoes, Photos and Info. Under "Info", I have a choice (presumably this is only available if Outlook is installed on the computer on which iTunes is installed) of sync'ing contacts, calendar and Outlook mail accounts with the iPhone, through iTunes sync. So, if iTunes develops instant amnesia, there is no WiFi sync.
I brought up Outlook because that is for what I use iTunes sync. The second one mentions Microsoft, everyone starts hyperventilating, leaping about and pointing fingers, like a bunch of demented Rumplestiltskins. Geesh.
I switched to iPhones in 2010 because Microsoft (watching them all start to prance about) stopped sync'ing Outlook with their mobile OS except through Microsoft Exchange, to force people into purchasing the très cher Exchange. OTOH, Apple still supports the sync. I love Apple very much (BFF status, really) when it works by WiFi. Not so much when the WiFi, she breaks.