Wow, this is some bad case law right here.
The Fourth amendment clearly holds here. If the police need a warrant to *tap* your phone line, then it stands to reason that the exact same information contained in the exact same device would equally require a warrant, or probable cause, to be searched.
Further, a modern cell phone quite literally contains one's "papers and effects" just as much as does a computer or filing cabinet. This is especially true here because the defendant was *in custody* having been found with illegal drugs on his person. A warrant would have been extremely easy to obtain with that kind of supporting evidence.