Abstract: Phosphate ore is an important non-metallic mineral resource used widely in agriculture, the chemical industry, medicine, national defense, and other fields, and magnesium removal is essential for its efficient utilization. Magnesium removal from coarse phosphate ore has the advantages of lower energy consumption and subsequent flotation pressure, but the current flotation-based magnesium removal methods still focus mainly on fine particle sizes. This is because good monomer dissociation of useful minerals is the premise for mineral sorting. On the other hand, the characteristics of traditional flotation machines limit the particle size of the feed, but high energy consumption due to grinding and deterioration of flotation from over-grinding have become important problems in mineral processing. With the development of fluidized flotation technology, fluidized bed flotation has attracted attention as a coarse-particle flotation technology. Compared with mechanical flotation cells, it is associated with lower turbulence and can significantly increase the upper limit of flotation particle size. In this study, the effect of fluidized bed flotation (FBF) on reverse flotation for magnesium removal from coarse phosphate rock was investigated by combining the separation test and scanning electron microscopy–energy dispersive spectroscopy (SEM–EDS) analysis to the underflow (–300+74 μm, P₂O₅ grade 27.20%, MgO grade 3.81%) from the mill of a phosphate concentrator in Yunnan Province. The collector dosage significantly affected the yield and grade of the product within a certain range in the process of FBF reverse flotation. Considering the agent dosage, product quality, and recovery rate, when the collector dosage was 500 g·t^–1, the magnesium removal effect was better, with concentrate yield of 43.63%, concentrate MgO grade of 1.68%, P₂O₅ grade of 31.72%, and MgO removal rate of 80.41%. SEM–EDS analysis further showed that FBF had a good effect on magnesium removal from coarse-particle phosphate ore. The MgO grade in FBF concentrate did not continue to decrease with collector dosage change due to the low degree of magnesium dissociation in the concentrate. The influence of phosphate rock particle size on the separation effect of FBF was as follows: the –250+125 μm fraction exhibited the best separation effect, with a better MgO removal rate and lower P₂O₅ loss; however, the –300+250 μm and –125+74 μm fractions had a poor separation effect. This was because the –300+250 μm coarse fraction was difficult to select, and the gangue removal rate was low, whereas the –125+74 μm fraction was greatly affected by the water flow, and the P₂O₅ loss was too high. Based on the test results, a new process of FBF pre-separation of coarse concentrate and FBF tailing re-grinding and re-separation was proposed. The MgO grade and P₂O₅ recovery of coarse concentrate could be adjusted based on feed particle size, with coarse concentrate and flotation machine concentrate blended into the final concentrate. This process could facilitate the pre-separation of 43.63% coarse concentrate from the underflow, which has the advantages of reducing energy consumption and reducing the pressure of subsequent flotation and dewatering. This study provides technical evidence in support for flotation-based magnesium removal from coarse-particle phosphate ore.