【Objective】The interaction between endophytic fungi and plants is affected by many factors, among which the content of phosphorus in soil plays a key role in regulating the interaction between them. However, it is not clear whether and how phosphorus fertilizer in the environment affects the interaction between endophytic fungi and plants.【Method】In this study, the symbiont of Phomopsis liquidambaris(B3)and rice(Oryza sativa L.)was used as the experimental model. Three different phosphorus levels, i.e., low phosphorus(LP), medium phosphorus(MP), high phosphorus(HP), uninoculated endophytes treatment(E-), and inoculation endophytes treatment(E+)were designed in this experiment. Physiological indexes of rice and B3 colonization were detected under different phosphorus levels to explore how phosphorus regulates the interaction between B3 and rice in the outdoor experiment and greenhouse experiment.【Result】In the outdoor experiment, B3 significantly(i)increased the phosphorus uptake ability of rice, (ii)promoted rice growth in the whole growth period and the formation of rice grain in the mature stage, and(iii)increased the rice yield by 7.05% under LP treatment. In MP and HP treatments, the effect of B3 was weakened. In the greenhouse experiment, under LP treatment, compared with the uninoculated treatment, the root/shoot ratio of rice inoculated with B3 increased by 22.48%, and resulted in an enhanced phosphorus uptake ability of rice by 39.98%. There was a significant enhancement of photosynthesis in rice and the accumulation of carbon sources such as sucrose, glucose and fructose in rice roots. However, the colonization of B3 was significantly limited under this condition. Also, consistent with this result, the biomass of B3 cultured in the LP medium was significantly lower than that in MP and HP mediums, which meant that B3 would be significantly affected by the phosphorus concentration. In the MP and HP treatments, B3 had high colonization in rice roots, but had little effect on rice growth.【Conclusion】Phosphorus concentration affects the symbiotic relationship between B3 and rice. In LP treatment, B3 colonization was low in rice roots, but it significantly promoted plant growth. In MP and HP treatments, B3 had high colonization rates in rice roots but with no significant effect on rice growth. Understanding the influence of phosphorus fertilizer on the interaction between endophytic fungi and plants will be helpful to improve the utilization efficiency of phosphorus fertilizer and microbial resources, which will provide a new path for the sustainable development of agriculture.