Nervous at work... how can I make this feeling subside?

Whenever I have to initiate a phone call or answer the phone at work, I get so nervous that I can actually feel erflies and get extremely nervous. The thing is, I am extremely articulate on the phone at home. I know it's because other people are around, and my boss sits really close to me. Therefore, I just feel EXTREMELY uncomfortable. Even if someone I know calls, I feel like I can't express myself, because I'm afraid someone is eavesdropping. It's really annoying. I know how stupid this is and I shouldn't feel nervous and just do what I gotta do, but I still do feel nervous..especially if nobody else around me is on the phone when I'm making a call, because I know everyone is listening.