Ambi Sitham told the court that she sat next to Rebekah Brooks at the meal in 2003 and that Brooks had suggested they keep in touch.
She told the jury she went to give her telephone number to Brooks.
"Piers [Morgan] turned to me and said 'Careful - she'll tap your phone'," she told the court.
Cross-examined by Clare Sibson, representing Brooks, Ms Sitham told the court she was "definitely a little bit concerned" by Mr Morgan's comment.
"I wasn't sure how serious the threat was," she added.
Brooks denies all the charges against her and the trial continues.
More top news
Slippy start tomorrow with frost & ice
The court will determine how much the UK government and travel firms knew about the risk of an attack on tourists holidaying in the area.
Car insurance for young people could rise by £1,000 a year after a change to compensation payouts for those with life-threatening injuries.