First install the iCalendar app from the DigitalBooker App Store (Administration > App Store)
* Copy the iCalendar webcal address from your DigitalBooker account (Administration > Locations or Employees)
* Open your iPhone's Settings
* Go to Mail, Contacts and Calendars
* Select 'Add account...'
* Select 'Other'
* Select 'Add Subscribed Calendar'
* Paste your webcal address that you copied above