iCal events on iPhone won't sync to MacBook Pro

I have an iPhone 4S, an iPad Mini and a MacBookPro. My iPhone and iPad are running iOS 6.1.3 and my MBP is running OS X 10.8.3. I also use iCloud to sync my Contacts, Notes, Reminders, Calendar events and other items.

When I sync my iPhone and my MBP, any events created in iCal on my MBP will sync to my iPhone and my iPad. But, any events created in iCal on my iPhone will not sync to my MBP. I'm pretty certain that it is only iCal events created on my iPhone that will not sync to my MBP, because creating contacts or reminders on my iPhone will sync to my MBP.

Any idea why events created in iCal on my iPhone will not sync with my MBP?

Thanks.