Patrick takes the position of the phone-answerer at the Krusty Krab in attempt to get a trophy, only for him to think the callers are asking if he's a Krusty Krab when they're really asking about the restaurant.
The phone rings a few times, but there is no one there.
The phone rings when Mr. Krabs and Plankton are fighting and SpongeBob responds to the caller by saying that Mr. Krabs isn’t available.
This phone is the subject of the "No, this is Patrick!" meme.