Phone System in Office 365 provides auto attendants, which can be used to let external and internal callers move through a menu system to locate and place or transfer calls to users or departments in your organisation.
An auto attendant is most often a node in a system, giving a caller a series of voice prompts or audio files they hear instead of a human operator. When people call a number associated with an auto attendant, their choices can redirect the call to a user or locate someone in your organisation and then connect to that user.