An experiment was conducted to assess interactive effects of temperature (22, 26, 30, and 34°C daily mean T) and phosphorus (P) fertilization (sufficient, 0.5 mM, and deficient, 0.08 mM P) on soybean physiological traits. The P deficiency decreased leaf P concentration over approximately 50% across temperature regimes. However, a marked decrease in physiological traits under P deficiency was primarily observed below and at optimum temperature (26°C) but not at warmer temperatures. This resulted in a significant P × T interaction for parameters such as net photosynthetic rate (PN), stomatal conductance, quantum yield of PSII (ΦPSII), and SPAD value. A combination of photo-biochemical parameters (e.g., ΦPSII, carboxylation capacity, SPAD value), improved CO2 diffusion processes due to unaffected or reduced mesophyll or stomatal limitation, and higher tissue P utilization efficiency appeared to overcome limitations to PN imposed by P deficiency at warmer temperatures.