How do I sync Windows Phone 8.1 to Exchange for calendar?

[Isaac Davidian]

My business uses Exchange, I use Outlook on my desktop PC. On my Windows Phone 8.1 (HTC One M8) all email syncs 2 way, contacts sync 2 way. However, calendar is one way only. My phone gets all calendar entries made on my desktop, but no calendar entries made on my phone are sent back to Exchange. I am using the email, contact and calendar apps that came on the phone.

Under Settings, email accounts, the Exchange account has all four of the "Content to Sync" boxes checked. However, I have never tried syncing tasks.