What can I fill in at Organization's phone number?

I just started working on my PMP application and one of the fields with which I am having trouble is "Organisation's phone number".
I work for an Organization of 3500 employees. There is no one phone number that anybody can call from the outside and get exactly the information that they are looking for. It is unlikely that if I provide a general public relations number, the person who answers will be able to immediately verify my identity. At the same time I don't know whether I can provide my superior's phone number since this is requested later in the application form. What should I do?