Routing and multicasting in ad hoc networks is a matured research subject. Most of the proposed algorithms assume a physically flat network architecture with mobile hosts having homogeneous capability in terms of network resources and computing power. In practice however, this assumption often may not hold true since there exist various types of mobile hosts with different role, capacity, and mobility pattern. In the military scenarios for instance, the leader of the troop usually has more powerful networking equipment than the private soldiers. In this paper, we consider mobile ad hoc networks that have physically hierarchical architecture where different types of mobile hosts form an ad hoc network hierarchy. We present a novel and simple multicasting framework called PHAM (Physical Hierarchy-driven Ad hoc Multicast) for ad hoc networks with such an environment. PHAM builds a multicast structure at each level of the hierarchy for efficient and scalable multicast message delivery.