Earlier quoted context omitted.
For phones to function they have to talk to cellular towers continuously. You can triangulate a location based on the chatter. Phone companies also keep detailed logs.
What about being made into listening devices? That would require turning on the microphone and transmitting the signal without the user noticing. Is that possible?
I don't know if that's what he meant by 'listening devices'. In any way, a lot of these statements make a lot of sense for many citizens in different parts of the world (China etc), where there's a corrupt government and a suppressed freedom of speech. For an US citizen I suppose they may be exaggerated. But I share many of his views, and he obviously deserves a lot more respect than some people show towards him.
EDIT. And of course, if it's running non-free software the cell phone can easily be made to transmit microphone data without the user noticing.