Today I found out my boss can listen to my calls

Today I found out my boss can listen to my calls After I answered and redirected a call to our store my boss called me and told me how I could have said something better and told me how I could have answered it. I suddenly became mortified at the realization that she must have been listening to me stutter and block. That in turn made me stutter more for the rest of the day. I'm so embarrassed and nervous. I want to get a different job so bad because I simply can't speak on the phone. I feel like my coworkers are listening and waiting for me to stutter and what if they ask me about it?!