Here's a step-by-step for setting up the calendar feed with the iPhone.
1) Go to Settings.
2) Scroll down and click on the "Mail, Contacts, Calendars" menu item.
3) Click on "Add Account".
4) Click on "Other".
5) Click on "Add Subscribed Calendar".
6) Paste the URL of your feed into the Server field.
7) Click "Next".
8) Now if you go to the "Calendar" from your iPhone home screen, you will see FlexBooker appointments populated into the calendar.
And clicking on one of those items in the list will show you more detail.