We often hear these words used interchangeably in common conversation. While this issue does not come up frequently, it is helpful to understand that certain terms have very specific meaning under US Copyright Law. Here's how the United States Copyright Office explains the distinction between a Sound Recording and a Phonorecord:
"A sound recording is not the same as a phonorecord. A phonorecord is the statutory term for a physical object that contains a sound recording, such as a digital audio file, a compact disc, or an LP. The term “phonorecord” includes any type of object that may be used to store a sound recording, including digital formats such as .mp3 and .wav files."