Yours, Etc.: Origins and Uses of 8 Sign-Offs
1845, "a written symbol," from phono- + -gram. From 1879 as "a sound recording."
phonogram pho·no·gram (fō'nə-grām')n.
A graphic tracing depicting the duration and intensity of a sound.
A character or symbol, as in a phonetic alphabet, representing a word or phoneme in speech.