The agency and BT will stop working together in September after PHD failed to convince Yell it could handle both pieces of business.
PHD's recent capture of the Pipex media account, another BT competitor, further complicated the situation.
BT is now reviewing its plans for replacing PHD. It is unclear whether it will call a pitch or hand the strategic planning to Starcom, which handles BT's buying and implementational planning.
PHD had tried to resolve the conflict by moving the BT business into a unit at its sister agency Abbott Mead Vickers BBDO (Campaign, 28 April). Yell is thought to have been unhappy with the solution.
PHD employs three planners on the BT business but is thought to earn a greater a fee income from the £19 million Yell account.
Morag Blazey, PHD's managing director of, said: "PHD has learnt a tremendous amount through developing communications strategy for BT. And I would like to hope that BT has benefited similarly from working with us."