I never thought of it like that. Very interesting, but I think there's more to it than an overdub.

Hello, I am new to the forum. I posted this question on the newbie forum because I am a newbie, and then I found musicians forum. My question, How is the guitar effected on the intro to the song ,Houses of the Holy, from the Physical Graffiti? Is it some kind of phase, flange? I appreciate any feedback or suggestions, because I have tried everything in my arsenal,to no avail. Thank you Zeppelin people.