I recommend しごとの日本語―電話応対 基礎編 for phone calls in business situations. We use some special expressions on phone conversations. For example, when we cannot hear the voice on the other end of line, we say 'ちょっとお電話が遠いようなのですが...'
Even for me, as a Japanese, it's a bit stressful to answer the phone in office, especially if he/she is a fresh recruit. But when you have learned some expressions, you won't feel any stress at all. This book is titled as basic, but the standard is very high. There is no furigana for most of the Chinese characters. And you have to have some knowledge of keigo before you try this book. But if you need or want to be able to talk on a phone in a business setting or formal situation, this book is worth trying.