Could you please tell me the meaning of "holding down the receiver" in this excerpt of The Great Gatsby, chapter 7?
“The rumor is,” whispered Jordan, “that that’s Tom’s girl on the telephone.”
We were silent. The voice in the hall rose high with annoyance. “Very well, then, I won’t sell you the car at all.... I’m under no obligations to you at all... and as for your bothering me about it at lunch time I won’t stand that at all!”
“Holding down the receiver,” said Daisy cynically.
“No, he’s not,” I assured her. “It’s a bona fide deal. I happen to know about it.”
Daisy is suggesting that Tom is not speaking into the phone but is instead speaking for the benefit of Daisy, Jordan and Nick. She implies that he wants them to believe that he is talking about selling a car, though this line of conversation is make-believe. She thinks that Tom is faking the story of the car to cover for a "real conversation" with his mistress.
The receiver here is the telephone receiver - the portion of the phone that one speaks into.
Nick knows that Tom is actually in negotiations to sell his car to George Wilson, the husband of his mistress. The reader discovers that Wilson plans to use the car to take Myrtle away because he has found out that "something funny" is going on with her. He suspects an affair of some kind, but does not as yet suspect Tom.
In the old days, when people did not have cell phones, holding down the receiver meant you were only pretending to talk on the telephone. When Daisy accuses Tom of holding down the receiver, she means she doesn't believe Tom is really having a conversation with Wilson. She believes Tom is faking the conversation as an excuse to stop by Wilson's garage so that he can visit Myrtle.
Daisy is wrong about Tom faking the conversation: Wilson really does want to buy the car, as we find out when the group stops for gas at his station on the way to New York City. Tom mentions the phone call and Wilson apologizes for having interrupted him at lunch.
However, Daisy's words are important because they suggest she now knows the identity of Tom's lover. This lends credence to those critics who believe Daisy deliberately steps on the gas when she sees Myrtle coming.