The hidden order phase in URu₂Si₂ is highly sensitive to electronic doping. A special interest in silicon-to-phosphorus substitution is due to the fact that it may allow one, in part, to isolate the effects of tuning the chemical potential from the complexity of the correlated f and d electronic states. We investigate the new antiferromagnetic phase that is induced in URu₂Si_2-xP_x at x ≳ 0.27. Time-of-flight neutron diffraction of a single crystal (x = 0.28) reveals c-axis collinear q_m=(¹/₂,¹/₂,¹/₂)magnetic order with localized magnetic moments (∼2.1-2.6 μB). This points to an unexpected analogy between the (Si,P) and (Ru,Rh) substitution series. Through further comparisons with other tuning studies of URu₂Si₂, we are able to delineate the mechanisms by which silicon-to-phosphorus substitution affects the system. In particular, both the localization of itinerant 5f electrons as well as the choice of q_m appear to be consequences of the increase in chemical potential. Further, enhanced exchange interactions are induced by chemical pressure and lead to magnetic order, in which an increase in interlayer spacing may play a special role.