The one who cleans offices is called an office cleaner. However, the American phrase is different. In the United States, Office Cleaners are known as Janitors who take on additional tasks such as focusing on sanitation (toilet) and kitchen regions. 

A janitor, in addition to cleaning, also performs security and repair duties. These are the responsibilities that a simple office cleaner doesn’t do. 

Other names for the office cleaner are the caretaker, housekeeper, and facilities manager.