I'm looking for something I can install on a Linux server to create a remote calendar that I can sync with my iPhone.
Anything requiring setting up an Exchange Server connection on the iPhone is out since I already have one set up for work. I'd like to avoid a groupware package since all I really want is a calendar.
As you are already syncing your iPhone with an Exchange server, you cannot use Activesync to sync a calender, as you can only have 1 activesync account on the iPhone.
This means you are limited to using CalDav (WebDav access to iCal Data). If you don't want the hassle of setting up your own server, you can sync Google calendar using CalDav.
If you want your own CalDav server some options are:
