You are screening your calls. If you had a secretary answering the phone, most likely she/he would screen your calls for you.
I screen my calls. If I am busy and my hands are physically occupied and I cannot answer the phone, the answering machine gets the call. However, being on the other end as the caller, I get tweaked when I call my kids and they don't answer their phones and I get their voice mail. They wait to see who is calling by the number on their phone. I have friends who never answer their phone and the machine picks up. Sometimes I think the "Never answer the phone" business is rude. Since I don't care for the "Never answer the phone" approach, I answer the phone when it rings, but I'm not going to break my ankle getting there.