Design noise-canceling headphones that are the size of a phone

I need noise-canceling headphones the size of a cell phone. I am trying to create a phone case that blocks out sound to the microphone. This is an anti-spying device to prevent the phone being used as a room bug. I have already tested noise-canceling headphones on a small voice recorder the size of a USB stick. And this worked. The problem is, a phone does not fit inside noise-canceling headphones. Hence, why I used a tiny voice recorder to test it out. So I need to take noise-canceling headphones, and make them the size of a phone, so that I can fit the phone inside. This would ideally need to be slim enough to fit in your pockets as well. As far as I can tell... you get X decibels of noise protection using FOAM.. and an additional Y decibels using a microphone/speaker that plays background noise inverted. This is how noise-canceling headphones work. So we need noise-canceling headphones, but that are large enough to fit a phone inside. I need you to design this product and show me how it would be made. Thanks.