What does Nick learn from Jordan when Tom is called on the phone?
When Nick goes lunch at Daisy and Tom's he gets a deeper look into their lives and gains his first glimpse into realizing everything is not as perfect as it seems. When the phone rings, Daisy tries to contain her composure and keep talking, but eventually she leaves the room to talk to Tom. When she leaves, Nick tries to be polite and carries on the conversation, but Jordan, straining to eaves drop on the conversation hushes him.
"Why-" she said hesitantly, "Tom's got some woman in New York."
"Got some woman?" I repeatedly blankly. Miss Baker nodded. "She might have the decency not to telephone him at dinner. Don't you think?"
By telling Nick about Tom’s affair, Nick learns not just about Tom’s indiscretions, but also about Jordan’s nosey, gossipy nature.