This is obviously a shortened version of asking, 'Is Mr Lee in?' It is not uncommon for people to drop the 'is' at the beginning of this question, but it is usually used in an informal way, especially if you are a regular caller. In those situations it is more common to use the person's first name, eg 'George in?'. I would be surprised to hear it used when making a professional or business call.
Sometimes only the vowel is dropped from 'is', then the remaining 's' is joined to the beginning of the persons name, so you hear something like, " 'sGeorge in?"
Telephone etiquette varies widely from place to place. Business calls are generally require more formal communication than calls to family or friends. Assuming a business or professional call such as this, I would normally expect the caller to say something like:
This is Dr. Anderson, can I speak to Mr. Lee please?
This is Dr. Anderson, is Mr. Lee available?