Dictionary.com
definitions

phono-

  1. a combining form meaning “sound,” “voice,” used in the formation of compound words: phonology.
Also especially before a vowel, phon-.
Compare -phone, -phony.

Origin of phono-

1945–50; < Greek, combining form representing phōnḗ voice
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018
British Dictionary definitions for phono-

phono-

before a vowel phon-

combining form
  1. indicating a sound or voicephonograph; phonology

Word Origin for phono-

from Greek phōnē sound, voice
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
Word Origin and History for phono-

word-forming element meaning "sound, voice," from Greek phono-, comb. form of phone "voice, sound" (see fame (n.)).

Online Etymology Dictionary, © 2010 Douglas Harper
phono- in Medicine

phono-

pref.
  1. Sound; voice; speech:phonometer.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.