US Customs and Border Protection agents have a wide authority to search individuals wishing to enter the country; more so than a normal police officer on the street does. While they can't legally force you to unlock your phone, they can repeatedly ask you to do it and seize your phone or detain you if you don't comply. They can also copy the data from your phone which, without encryption, is pretty much just as good. A new bipartisan bill introduced yesterday by Senator Ron Wyden of Oregon would change all of this. The summary is as follows:
To ensure the digital contents of electronic equipment and online accounts belonging to or in the possession of United States persons entering or exiting the United States are adequately protected at the border, and for other purposes.
The "Protecting Data at the Border Act" would require border agents to get a warrant based on probable cause before they searched any device. Right now, agents don't need a warrant or even a suspicion of wrongdoing. The findings of the bill conclude that "United States persons have a reasonable expectation of privacy in the digital contents of their electronic equipment."
This statement was echoed by Senator Rand Paul of Kentucky who added that "Americans should not be asked to surrender their rights or privacy at the border, and our bill will put an end to the government's intrusive practices." The bill only applies to US citizens though, so foreign travelers don't get any of the proposed protections.
The issue of digital privacy along the borders has gained attention lately following a high profile incident in which a NASA scientist's phone was seized at an airport. The Department of Homeland Security has also had its own share of privacy concerns. Border agents only search a fraction of a percent of phones, but that number is growing. There were only about 4,500 searches in 2015, but 2016 saw a jump to 23,000 searches.