Soybean is a globally relevant agricultural crop, essential for food production and industrial applications. The efficient management of phosphorus in the soil is crucial for root development and biomass formation. However, the efficiency of phosphorus use in soils with variable fertility remains a challenge for countries with tropical soils. In this context, BiomaPhos, an inoculant developed by EMBRAPA in Brazil, registered for use in corn and soybeans, contains phosphate-solubilizing microorganisms, specifically Bacillus subtilis and Bacillus megaterium, which aims to improve phosphorus availability in tropical soils, where this nutrient is often immobilized. BiomaPhos is widely used in Brazil and also has a potential impact on global agriculture. This study aimed to evaluate the effect of different doses of phosphorus, with and without BiomaPhos, on soil organic matter in soybean crops. The experiment was conducted in a field with a split-plot design and by considering two factors: inoculation with BiomaPhos and phosphorus doses (0%, 50%, and 100%). Soil samples were collected after harvest and analyzed to measure organic matter. Statistical analyses included the calculation of means, standard deviations, and comparisons using t-test to identify significant differences. Soil organic matter means were consistently higher without BiomaPhos at all phosphorus doses. The mean organic matter was 73.75% and 73.00% for the 0% and 50% doses without BiomaPhos, respectively, compared to 69.00% and 62.75% with BiomaPhos. At the 100% dose, the means were 67.50% without BiomaPhos and 64.75% with BiomaPhos. The results show that although BiomaPhos increases phosphorus availability, it also reduces the percentage of organic matter in the soil, regardless of the dose applied. This reduction suggests that BiomaPhos may be affecting soil dynamics in a way that is not conducive to the conservation of organic matter. Since organic matter is essential for soil fertility and structure, this change may have implications for long-term soil health.