There is a phone located on desk 434, which is just outside Stanley's Office, where you may receive three random calls from either his wife, a Future Happiness Foundation employee, or a random stranger. Answering the call from the Future Happiness Foundation will make the office full with cardboard boxes upon beginning the game again.
Another phone serves as a Point of Divergence. After you ride the cargo lift in the Warehouse, you are taken to the Phone Room where a phone is presented. If you pick it up, you will be taken to the Phone Ending. But if you decide to unplug the phone, you will end up in the Not Stanley Ending.
This object can lead to the Not Stanley Ending and the Phone Ending.