"Speak Passphase aloud" is a mission objective in the quest Dwarven Allies in Tiny Tina's Assault on Dragon Keep DLC
After placing the letters from left to right to spell out "Fart" head to the middle and interact with it to speak the phase
Vault Hunter: "Uhm ... raft."
Lilith: "Was that not the password?"
Mordecai: "Ugh, god ... I just figured it out."
Brick: "So say it."
Mordecai: "Fine. It's (sigh) ... 'Fart."