Dom Loehnis, Mr Cameron's close friend, asked Brooks whether Coulson could survive press speculation and keep his position at No 10, the court heard.
Mr Loehnis, who works for a headhunting firm, told the Old Bailey that she said she was unsure he would survive. During a brief chat, Mr Loehnis and Brooks agreed that the breaching of smartphone voicemail security was common knowledge.
The PM's friend told the court that Brooks never spoke about the 2006 case or said that she was aware of the phone hacking.
Jonathan Laidlaw, for the defence, asked Mr Loehnis: "Did Brooks say nothing to suggest she had been involved in phone hacking while she was the editor of the newspaper?" "No, she did not," he said.
Jurors heard evidence about a lunch attended by Eimear Cook and Brooks. The lunch was held at the London home of Joanne Manoukian and Rafi.
Mrs Cook said on Monday that Rebekah Brooks remarked how easy it was to monitor cell phone voicemails. But Brooks said she did not talk about hacking phones at all. Mrs Manoukian backed up her statement, saying: "I don't remember us talking about phone hacking."
The trial is still ongoing.