The court is not interested in your passphrase, they want the information that it is protecting. The court will simply compel you to provide the information in another manner if you claim that revealing your passphrase would be a 5th amendment violation (although I doubt they would even buy that one to begin with.)
1) tell you to provide the pass phrase to your lawyer (which makes it protected via attorney-client privilege) and then tell your lawyer to unlock the system and provide it to the court
2) out-geek you and notify you that since your encryption system does not actually use your passphrase but instead passes it first through a strong hash function you are to provide the court with the hashed passphrase so that they can use a decrypt method which skips the hashing step.
The short version is that claims that a passphrase alone is protected via the 5th is unlikely to succeed.
1) I read about at least one case where that's about what happened. The police asked the defendant to unlock the computer; they didn't ask for the password itself.
1) tell you to provide the pass phrase to your lawyer (which makes it protected via attorney-client privilege) and then tell your lawyer to unlock the system and provide it to the court
2) out-geek you and notify you that since your encryption system does not actually use your passphrase but instead passes it first through a strong hash function you are to provide the court with the hashed passphrase so that they can use a decrypt method which skips the hashing step.
The short version is that claims that a passphrase alone is protected via the 5th is unlikely to succeed.