To manually clear all existing Calendar Events on your Android Phone, perform the following steps. This may be necessary if your Android phone's Calendar has stopped syncing to your GMail Calendar.
Access "Manage apps"
Locate "Calendar Storage" and open it
Click "Clear Data" to clear the existing Calendar data
Note, after clearing your Android Calendar, it may take a couple of minutes for your Android Calendar to re-sync to GMail. It may also be necessary to uncheck and check the "Sync Calendar" option in phone's Account Manager, as doing this will automatically force your phone to perform a new sync.