Whenever you're leaving a phone message, you should speak clearly, spell your name, state your purpose, and: C. Leave your phone number. That is the professional way. Hope that helps.
In any form of effective communication, like in the case of one leaving a phone message, it is of the utmost importance to make sure that the receiving end of the communication is provided with the necessary means to reply to your message or request. Failing to do so would, evidently, short circuit the channel of communication, or in other words, it would impede the conversation from continuing.
