https://www.techradar.com/news/your-phone-location-data-requires-a-warrant-rules-the-us-supreme-court

In an clear win for proponents of data privacy, the Supreme Court issued a decision that requires law enforcement to obtain a warrant to track individuals through cell records “in the rare case where the suspect has a legitimate privacy interest in records held by a third party”. 

It’s not a complete protection, but it goes a long way toward setting precedent that cell phone data should be protected by the Fourth amendment.