The Royal Instrument of Summoning is a phone-like instrument with which Princess Nautilus summons Liquus. It is first found by Cucumber, who offends Nautilus by calling it a cell phone. Nautilus insists that it is nothing like any sort of phone.
King Kelp taught Nautilus how to use the Royal Instrument.
The Royal Instrument broke because Panpipe accidentally crushed it. Nautilus was very saddened about this. It was upgraded into a nicer smartphone model.