Differential Scanning Calorimetry (DSC), Thermogravimetric Analysis (TGA), and Impedance Spectroscopy (IS) were used to study the phase behavior of the system, NaH2PO4.H2O above room temperature. The DSC results show five endothermic anomalies with picks around 70 oC, 120 oC, 210 oC, 325 oC and $350 oC, during the first heating run, but any anomaly is show on the subsequent cooling run. The TGA results show that fresh powder of NaH2PO4.H2O loss weight when the sample is first heated across the different temperatures. The electrical resistance of fresh sample NaH2PO4.H2O also shows strong variation at 70 oC and 120 oC anomalies, indicating that the ionic transport is enhanced between 50 oC and 108 oC, and between 120 oC and 150 oC. We discuss and attributed the observed behavior in NaH2PO4.H2O throw the different temperatures, where observed the anomalies, as a consequence of a dehydration process of the sample.