Yes - and he is right. The phone is in permanent connection with the network anyway - it's some code away from opening the audio to listen to your room conversation.
My name begins with the letter A, so I get quite a few accidental calls when someone leaves their phone unlocked in their pocket.
Mostly you just hear an incomprehensible garbled rustling noise.
Spying on someone by remotely turning on the phone in their pocket isn't usually going to work.
Although you are correct about the pocket thing, the point is that you don't know when someone may be listening to you.
Sometimes it's not. But if you're determined enough to spy on somebody via the audio on their phone, you will likely be persistent and eventually overhear something the person would prefer you didn't. If I were concerned about being spied on I wouldn't dismiss it so easily.