Predicted equilibrium PH₃ abundance in the presence of different metal-phosphorus species ([Fe/H] = −0.5). (a) Temperature–pressure profile from the Sonora models for T_eff = 750 K and log(g) = 4.5. (b) Mixing ratio of PH₃ as a function of pressure. (c) Mixing ratio of PH₃ as a function of temperature. Different colors represent different metal-phosphorus species introduced into the model. The gray dashed line represents the case when no metal-phosphorus species are present (NM: no metal) or the metal-phosphorus species fail to condense (labeled “others”), such as Mg, Al, K, and Ca.