The 4th ammendemnt is the one that protects your data and other possessions in general, not the 5th. The 5th protects you from being compelled to give testimony that might incriminate you, which then protects you from being compelled to offer a password to access data that could be used to incriminate you.

Since 4th ammendemnt protections are significantly curtailed at border crossings, they can actually declare on the spot that your data is now their data. The only thing they can't do is force you to tell them how to access it - but, if they can hack your password, they actually have the right to search your phone just as much as they have the right to search you luggage.