I disagree with your proposition that this was a liberal decision. As a fairly conservative guy, I believe that the decision represented a clear victory for the 4th amendment. I do not think that the supreme court can or should make decisions that conflict with the constitution. If you don't like what the constitution says, there is a process to amend it.
IMHO, the 4th amendment is black and white clear in this case:
"The right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures, shall not be violated, and no Warrants shall issue, but upon probable cause, supported by Oath or affirmation, and particularly describing the place to be searched, and the persons or things to be seized."
My phone is one of my "effects" that is constitutionally protected. The data within my phone (or that is generated by use of my phone) is also protected as it is an integral part of my effect (my phone).