[CalendarServer-users] Check Availability - iPhone or Web clients?

We are running Server.app 5.2 on macOS 10.11.5. In the Mac based Calendar client there is a ‘Check Availability’ button that can be used to verify the schedule of an invitee for their free time. Is there any way to ‘Check availability’ of an invitee using the iOS Calendar app? Is is possible to do so with Server.app’s web client, and if not, are there any other web based calendar clients that are known to provide this functionality? Thanks in advance Ian