No private Events with Caldav

We are using normal iPhone Calendar App with caldav integration and caldav.

It is not possible to change the privacy Status of an event in iOS app. I can not declare a event as only visible for me and busy for others. I need to login to NC Website to configure that. Is that a wrong configuration of our cloud or is the iOS app missing a feature. Is there another Calendar App where i can flag my events as private and busy for others? A friend of mine had that on Android too but he could solve it with changeing the Calendarapp