The privately owned company centralised its media into PHD almost three years ago, but will conduct the review as part of its practice of regularly looking at suppliers.
Other agencies will be contacted in the run-up to a formal pitch in November.
The task covers the Weetabix brand as well as Alpen, Alpen Bars, Mini Crunch, Ready Brek and Weetos. Weetabix spends £5 million on the main brand and more than £4 million on Alpen and Alpen Bars. Alpen Bars were its biggest recent launch, backed by a £2 million media spend.
PHD was appointed in December 2000 to handle the centralised Weetabix media account. It was previously split between PHD and Western International Media, prior to Western's merger with Initiative Media.
Banks Hoggins O'Shea/FCB handles creative for Weetabix. Its hold on the account is unaffected by the media review.