It was Reich's first attempt at applying his "phasing" technique, which he had previously used in the tape pieces It's Gonna Rain (1965) and Come Out (1966), to live performance.
It represents a transitional stage in that it combined, in its original version, live instrumental performance and tape accompaniment.
Already with the publication of his collected Writings about Music in 1974, he excluded it from the compositions he regarded as "worth keeping", and never mentions the work in that book, even in passing.
[4] The limited harmonic material aside, Reich had come to realise that unusual numbers of beats, such as the quintuple meter of Reed Phase, offered less than they initially suggested.
[8] The composition is based on a five-note cell, or "basic unit", which is repeated continually throughout the entire work.
The basic unit is continually repeated by the instrumentalist and, because the performer must play without any interruption for at least five minutes, Reed Phase requires the use of circular breathing, instructions for which are given in the score.
[1] The reed instrument recorded on the tape repeats the basic unit in a fixed tempo, while the instrumentalist begins a cycle of phase shifts consisting of the soloist repeating the basic module a certain number of times, then accelerating the tempo until the shift against the steady part (tape or accompanying reed instrument) is increased by one eighth note, and then resuming the initial tempo for a certain number of repetitions in a constant relationship with the tape.
At this point, the second channel fades out and the soloist continues the third section as a repeat of the first, until coming back into phase with the tape once again.