The PHENIX experiment has measured identified hadron spectra (pi, K, p and pbar) in Au+Au collisions at sqrt(s_NN) = 200 GeV. At low pT (< 2 GeV/c). The spectra are well described by the hydrodynamic framework, and the statistical thermal models reproduce the measured particle ratios. The bulk properties of the hot and dense matter at RHIC can be extracted, such as chemical and freeze-out temperatures, expansion velocity, and baryon chemical potential. During the past three years of RHIC runs, PHENIX has also measured the identified particle spectra in p+p, d+Au, Cu+Cu, and Au+Au (62.4, 200 GeV). These data provide a unique tool to characterize the bulk properties and of matter and their evolution. In this talk, we will present systematic studies of particle production as a function of beam energy, collision system and centrality. We will also discuss the systematic study of baryon production at intermediate pT and implications for the puzzling baryon anomaly at RHIC.