The yearly phosphogypsum (PG) production is significant, posing technical and environmental challenges for its permanent stacking. However, within the context of the circular economy, the value-adding of this coproduct in civil engineering, particularly in the construction of roads, is a viable option. Positive mechanical (by deflector) and environmental (by leaching test) evaluations were made possible by the first experimental one-kilometer-long pilot project, constructed at Safi, Morocco in 2017. It included four distinct PG-based formulations with a 7% cement addition. To further assess the feasibility of using PG as a road material, our experimental approach here focuses on material mixture optimization—made of phosphogypsum (maximum content desired) treated with cement (to be minimized to reduce the cost) and sand or steel slag as granular corrector to meet road mechanical requirements. Phosphogypsum made at the Jorf Lasfar plant and other materials were first identified and characterized. The design of experiment method is used to simulate the desired mechanical and physical responses and to identify domains that satisfy the requirements for using the mixed material as the foundation layer or as a subgrade layer for roads. Furthermore, using a parametric analysis, we assessed the influences of traffic level, soil bearing capacity, and mechanical performance of treated phosphogypsum mixtures on pavement design for three distinct pavement structures (mixed, reverse, and structure with treated sub-base) and concluded that the pavement structure with subbase treated with hydraulic binder is the best to adopt for maximizing PG (phosphogypsum) recycling.