Sync eGroupware with Apple Calendar

Go to Calendar -> Preferences -> Accounts, then click on the plus sign to add a new account and choose Other CalDAV Account.

Select Account Type -> Manual and enter your D-PHYS username and password. For the Server address use

Under Calendar -> Preferences -> Accounts -> Delegation you can toggle the view of other D-Phys calenders for which you have access rights. Alternatively you may add them as separate accounts by providing the full path as Server address