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Efficient and fair resource allocation in cognitive radio (CR) networks under strict constraints imposed by the primary network is a challenging problem for underlay dynamic spectrum access (DSA) networks. Due to the distributed nature of secondary networks, traditional approaches are usually computationally inefficient in providing fair resource management while meeting severe constraints imposed by the primary network. In this paper we consider the scenario of homogeneous CDMA-based DSA network with one main primary receive-transmit pair and an arbitrary number of secondary users (SUs). Unlike the prior works, we consider the case where SUs can adaptively adjust their transmit directions besides transmit power according to available channel information. For such a scenario, we formulate the joint power allocation and phase control problem and find the optimal solution to maximize the total rate for the secondary network subject to interference and power constraints. Our method has a linear computational complexity and guarantees fairness among SUs. Numerical analysis show that introducing the phase control alleviates the restriction of strict interference constraint while keeping the efficiency of power allocation.