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
It ends a political standoff that briefly saw Yahya Jammeh and Adama Barrow claiming leadership of this tiny West African nation.
Britain is braced for sub-zero temperatures expected to bring 'harsh frost' through next week.
The historic moment was watched by 500 people in the Church in Wales who cheered after the ceremony.