The insurance arm of the Prudential previously used PHD to handle planning and buying for its £1 million motor insurance account.
MediaCom won the business without a pitch. It was appointed by the Royal Bank of Scotland division UKI Partnerships, which runs Prudential Insurance.
The decision to move the account to MediaCom does not affect PHD's hold on the corporate planning and buying account for Prudential.
Prudential Insurance uses press to advertise its motor insurance products but has plans to market other insurance offers such as household.
UKI Partnerships was launched in 2000 and also manages Green Flag's roadside service and NatWest's home insurance scheme.
Creative for the Prudential Insurance account, which is held by WWAV Rapp Collins, was not part of the review.
The Prudential win follows MediaCom's capture last week of the Churchill Insurance account from Carat.
Nobody at MediaCom was available for comment.