Are smartphones listening in? Yes, but normally they are triggered by a keyword or key phrase. Like when you use Siri. Is it nefarious? Mostly it isn't. These are automated systems that mine some commercially useful data. Abuse can't be ruled out, however. Do you trust Google, Facebook, Twitter etc? Turn off Siri, Google OK, and Cortana. Various agencies can use your phone as a listening and tracking device whether or not the voice feature is on or not. If, and let me play the pronoun game, "they" are after you, humans will be the ones analyzing the gathered data. Paranoia is a trigger for self-fulfilling prophecies.