Most of the marine phosphate deposits are calcareous phosphates. Calcination process is one of the famous processes used for upgrading sedimentary calcareous phosphate ore. In this study, evaluation of the calcination process performance in terms of its operating parameters was carried out. The effect of operating parameters and their significance on calcination of calcite as a main phosphate ore impurity was studied using statistical design of experiments. A statistical model was developed to correlate the studied parameters with the phosphate grade in the calcined product. The studied parameters were temperature, time, and particle size. The analysis of the design results showed that the temperature is the most significant parameter. The higher the temperature is the higher the calcite conversion to calcium oxide and release of carbon dioxide. In addition, the particle size plays a significant role in contact area between particles as well as the voids among them that help to release the CO 2 faster. Moreover, a phosphate concentrate, suitable for phosphoric acid production, containing ∼32 % P 2 O 5 can be achieved at optimum values of studied parameters, i. e., at a temperature of 850 °C, after a calculation time of 40 minutes and with a particle size of 0.074 mm, respectively. Furthermore, quenching and slacking of calcined products increased the grade by 2–3 % to reach 34 % to 35 % P 2 O 5 in the final concentrate.