The porous Phosphine Coordination Material, PCM-10 contains abundant free P(III) donor sites that can be subjected to a variety of post-synthetic modifications. The diverse P(III)/P(V) organic reactivity and coordination chemistry available to aryl phosphines have been exploited to decorate the pores of PCM-10, allowing for an extensive structure function study. Polar P=O moieties, charged P+-CH3 phosphonium species with exchangeable coanions (I-, F-, BF4-, and PF6-) and P-AuCl groups have been successfully post-synthetically incorporated. These modifications directly affect the strength of the resulting host-guest interactions, as demonstrated by comparative sorption studies of CO2, H-2, and other gases in the solid-state. Broad tunability of the enthalpy of CO2 adsorption is observed: incorporation of BF4- ions inside the pores of PCM-10 results in 24% enhancement of the isosteric adsorption enthalpy of CO2 compared to the parent material, while F- anions induce a 36% reduction. Meanwhile, AuCl-decorated PCM-10 shows a high H-2 sorption capacity of 4.72 wt % at 77 K and 1.0 bar, versus only 0.63 wt % in the unmodified material.