As long as the person is listed in the phone directory, it is possible to look up the address online, using the person's phone number. Some people choose not to be listed, so it's not possible to use their numbers to find their physical addresses.
A reverse phone number search allows the user to find out a person's name and address based on phone number alone. This works for individuals as well as businesses, as long as they are publicly listed. The reverse is also true. The user can search using someone's address and find out the person's phone number if it is listed.