Bash'ir Phasing Device

The Bash'ir Phasing Device is a quest item used on the quest. Players must kill ethereals until one of the phasing devices drops, then use it so they can see the on the ground.

Once activated, any party members/pets within 100 yards gain the 'out of phase' property (as described under "use" in the tooltip). Such other people can exit and reenter at will.

You retain this buff at any altitude - you can climb to the flight ceiling and still be out of phase. However, leaving the area of Bash'ir Landing will strip you of the buff. (All party members out of phase due to your having used the device will likewise be stripped of the buff.)

Source
The Bash'ir Phasing Device drops from all ethereals at Bash'ir's Landing.