Telephone etiquette means being respectful to the person you are talking with, showing consideration for the other person's limitations, allowing that person time to speak,communicating clearly and much, much more.
Your voice must create a pleasant visual impression over the telephone.
Good phone etiquette is important because we cannot see the facial expressions and body language of the other person and they cannot see us.
We must compensate by choosing our words carefully and using much more tone inflection to convey our message than if we were face to face.