This article presents an accurate phase response control (APRC) algorithm to realize directional modulation (DM), improving the physical layer security of Internet of Things (IoT) networks. Specifically, the concept of normalized array response control is developed to realize the phase response control, and the designed weight vector is constructed as the sum of an initial weight vector and an appended weight vector. The precondition of precise phase response control is theoretically derived, and a geometric interpretation of phase response adjustment is given. The APRC algorithm can derive an analytical solution to realize the precise phase response control and normalized magnitude response control jointly, and the computational complexity of the APRC algorithm is much lower than the existing approaches. Moreover, a flexible DM scheme based on the APRC algorithm is presented to realize the specific PSK symbol synthesis. Different from the existing works that are only feasible for the single direction PSK modulation design, the APRC algorithm is applicable for the more general multipath and quasistatic block Rayleigh channels. The synthesis results with fixed and random initial weights are illustrated to show the wide applicabilities of the APRC algorithm, and the bit error rate simulations are given to validate the APRC algorithm.