You might want to be a bit more specific in what you're trying to accomplish, but this is what I'd suggest:
Either 1) Choose not to sync a certain calendar (or all calendars) in the iPhone's iTunes preference window. Or 2) delete the calendars directly in iCal before syncing the phone.
There is no way to delete an entire calendar on the iPhone. You can only delete one individual event at a time unless the event is scheduled to repeat, in which case it will promt you to delete "all future" recurrences of that event.
Hopefully that helps, if not, just be a little more specific.