Why can't I hear my own voice when using my phone headphones?

Episode 1454 (1:49:30)

Ken from Tustin, CA

Ken wants to know why he can't hear himself when he speaks with headphones? Leo says he'd need a mixer that can mix in. It's called Side Tone. It can be very distracting with Bluetooth on a phone though because of the latency. He would just end up getting confused by the echo.