In the middle of the fourth floor, just to the left of James' room, there's an invisible phone. It's fully functional and can be used just like the regular phones.
The Japanese version of the game is a licensed title based on the 1986-87 anime adaptation of the 1949-55 manga Anmitsu-hime (Sugar Princess), with the goal of navigating Princess Anmitsu across Japan to a cake shop before it closes.