The pressure-dependence photomodulation spectrum of a semiconducting conjugated polymer, phenyl-substituted ladder-type poly(para-phenylene) (Ph-LPPP) with trace-concentrations of metallic impurities, was studied. The so called photo-induced absorption gave the information about the triplet-triplet (TT) transitions and bleaching (PB) of the singlet state in this material. Planarization, therefore, stronger interchain interaction, under pressure was observed. The photo-modulation spectra coupled with Raman scattering and photoluminescence spectra of Ph-LPPP revealed the influence of electronic structure due to pressure on singlet and triplet excitons. As a result, the localized character of triplet state could be changed. The lifetimes of the triplet excitions and the photobleaching were also observed. It was found that the triplet state was less stable than the singlet state.