I have shared some calendars that I maintain in a Mac. For several months these calendars appeared normally on both the iPad 2 and iPhone 4S. Then something happened--we do not know what--and all the shared calendars dropped off the two iOS devices. From the Mac, then, I sent new invitations to these calendars, and the iOS user accepted them. Now these calendars appear on the iPad but not the iPhone.
I do not know if it matters, but the iPhone is still on 7.0.6, because the iPhone does not have enough available memory for the upgrade to 7.1.