Seeking Advice: Need help with soundproofing my wall

The situation is that when speaking to friends on the phone or online, the fairly hollow wall between my room and parents room (other side) allows sound to go through. This upsets my parents and myself as it's a pain for us both. The wall in front of my desk is the hollow one which I believe let's sound through the most, the one on the right of me is a solid brick wall which I don't think let's much sound through. What would be the best course of action/method to soundproof my wall so I'm barely audible. Even speaking quietly can apparently be heard before anyone says to whisper