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