To party: "You see Jericho standing still as a statue, there is a look on his face that is a combination of fear and pain. His eyes seem to be out of focus as though looking at something a few inches in front of him."
To Jericho: "Out of the ground, the air, all around you a hazy image starts to form. There is a shrill hum that pierces your ears, but it is more like it's in your head. Screams and cries, howls and snarling, all eminate from this image, the sound so overwhelming it drowns out the world. The image shifts, demons, terrifying monsters, nightmares, fears, all appearing and disappearing as you shift your gaze. "
Jericho cannot leave the area himself as he's restrained, but he can lash out which may cause him to penetrate the illusion causing the psychic damage.
His party can try to call out all they want, it'll have no effect, and if they try to move him he'll take the psychic damage.