A rapid population growth in Côte d’Ivoire, notably in Man, leads to progressive degradation of agricultural soils, amplified by a heavy reliance on chemical fertilizers. To address this, the study evaluates the agronomic performance of three different bio-phospho-composts made from varying doses of Moroccan phosphate rock (150, 300, and 450 kg/ha). Field trials were conducted over three cycles to determine their effects on the agronomic parameters of rice and maize. Results show that, under high doses of phosphate rock (RP) (T3 to T6), grain yields range from 3.5 to 5.5 t/ha for rice and 3.93 to 5.5 t/ha for maize. Conversely, low RP doses (T1–T2) produce grain yields from 1.77 to 2.79 t/ha for rice and 1.77 to 3.5 t/ha for maize. The association of biofertilizers with chemical fertilizers (KCl, urea) strongly increases all agromorphological parameters (p < 0.0001) compared with treatments without chemical fertilizers (T2, T4, T6). However, treatment T6 with 450 kg RP/ha, without chemical fertilizer, shows an even more marked improvement, surpassing treatments with chemical fertilizers (T1 and T3) and recording a relative yield increase (TAR) of 319.76% compared with T0 under T6. Under T1 and T3, TARs are 179.89% and 295.52% respectively. The 450 kg RP/ha dose appears optimal for increasing the productivity of rice and maize. The study highlights the need for dynamic and crop-cycle–specific fertilization management to ensure sustainable production.