Phoebe Bridgers wore an outfit not safe for prime-time television, but perfect for the premiere of “Primetime” at the Venice Film Festival … stunning in a sheer gown that left little to the imagination.

The singer-songwriter walked the red carpet at the movie’s premiere Saturday … wearing a blue dress that looked more like a nightshirt than a formal gown.

The flowy, baby blue number revealed Phoebe was only wearing a pair of black underwear beneath — without a bra … letting the whole world see behind the curtain.

As you know … the four-time Grammy winner is making her first real feature-film debut in “Primetime” — the upcoming flick which stars Robert Pattinson as a fictionalized version of “To Catch a Predator” host Chris Hansen.

Bridgers is playing Del … a member of the “decoy team” who pretends to be a minor to catch potential pedophiles. Phoebe has previously made cameo appearances as herself in “Between Two Ferns: The Movie” and “I Saw The TV Glow” — so this will be her first time playing a character.