Android calendar won't sync with Office 365

Hello,

I have successfully been using Office 365 with Outlook 2010 and a Samsung Galaxy S3. However, I now notice that when I create an calender entry on the android phone, this entry does not sync with Outlook 365 on the web or my desktop-based Outlook 2010. In contrast, when I create a calendar event from the desktop or from the web, the event does synchronize with the android.

The problematic direction is Android ----> Desktop/Web.

I am not an IT pro. Could anyone please offer a simple resolution to fix this?

Thanks.