The Li4P2O7 and Li2Cu2P6O18 phase formation and its correlation with luminescent properties in Cu+ doped Li3PO4 were studied. The study shows that in air annealed samples minor phase of Li4P2O7 along with Li2Cu2P6O18 is formed. The amount of Li4P2O7 is inversely proportional to the annealing temperature whereas amount of Li2Cu2P6O18 increases with annealing temperature. These phases affect luminescence properties of the material significantly. The Cu+ luminescence decreases with the increase in Li2Cu2P6O18 whereas, the TL–OSL sensitivity is found to be a function of amount of Li4P2O7 phase present in the sample. Of the sample annealed at various temperatures maximum OSL sensitivity is obtained for the 600°C annealed sample for which 20% Li4P2O7 phase is detected which is maximum among all air heated samples. The minimum sensitivity is observed in case of sample melted in air in which 3% of this phase is detected. Vacuum heated sample also shows minimum sensitivity, in which no Li4P2O7 phase is detected.