No Fourth Amendment in American airports?

In England there is no Fourth Amendment and they can search your phone when you land. The Supreme Court has never ruled on your Fourth Amendment rights as they specifically relate to your cell phone at American airports/border crossings. But somehow an American in an American airport on American soil has to surrender his rights to an American customs agent? The Supreme Court has ruled on Fourth Amendment exceptions at border crossings, but not cell phones in particular. Your Fourth Amendment rights do not defy gravity there.