A phaser is an effect you can use on a guitar (or any other instrument/sound signal). Bernie probably had a pedal; you can process the sound through a phaser effect on the computer nowadays. I've used it but it never sounded anything as cool as the opening chords of TIE. I think the double tracking is maybe what gave the sound such an expansive and exciting feeling. It doesn't get old! I still feel that excitement when I hear that song. Well done, Bernie!