In the present work, the phase formation and thermal evolution in phosphorus-doped BaTiO3, have been studied using differential thermal analysis, X-ray diffractometry, scanning electron microscopy coupled with energy-dispersive spectroscopy, transmission electron microscopy, and high-temperature nuclear magnetic resonance. Phosphorus cations that are incorporated from ester phosphate form a surface layer that covers the BaTiO3, particles. This layer acts as a reactive coating during sintering. Phosphorus-doped BaTiO3, samples that have been treated at temperatures of 650 degrees-900 degrees C show the presence of crystalline Ba2TiP2O9 and/or Ba-3(PO4)(2) phases. The appearance of secondary phases is dependent on the cooling rate. Higher temperatures (900 degrees-1200 degrees C) result in the presence of a phosphorus-BaO-rich phase that covers the BaTiO3, particles. As a consequence, the remaining titanium-rich BaTiO3, drives the formation of a liquid phase at temperatures >1200 degrees C. In regard to the reported sintering behavior of P5+-doped BaTiO3, the formation of a phosphorus-BaO-rich phase that covers the BaTiO3, particles could be the origin of the improved porosity coalescence and removal that is observed at the earlier stages of sintering.