The Phase Blade is a tool useful to those who travel in the Ethereal Plane of Atrii. This blade, blazing like a rainbow, can be used to cut through particular routes of travel on that plane which are blocked by vague outlines. But in this plane of existence a phase blade is virtually useless, and appears as nothing more than a vague outline that disappears the moment one sets their eyes on it.

In 966 GUE, Phase Blades were selling for about zm40.

SOURCE(S): Beyond Zork