The G338 ionomer glass is a fluoro-alumino-silicate system, which is used as the powder component of glass ionomer cements (GICs) in dental applications. However, despite progress in understanding the nature of this glass, chemical identity of its separated amorphous phases has not yet been conclusively determined. In this work, we identify these phases by performing differential scanning calorimetry (DSC) and X-ray diffraction (XRD) analyses on both the as-received glass and heat-treated samples. We detected three glass transitions in the as-received G338 glass during DSC upscanning, implying the co-existence of three amorphous phases. Towards resolving the chemical identity of the three phases, we performed XRD analyses on samples subjected to dynamic heating, while further DSC and XRD analyses were performed on samples subjected to isothermal treatment. The results suggest that the three amorphous phases in G388 are Ca/Na-Al-Si-O, Ca-Al-F and Ca-P-O-F phases, respectively. However, the exact chemical compositions of the three phases still require further exploration. The results of this work are important for understanding the impact of phase separation within ionomer glasses on the setting behavior of GICs, and hence improving performances of GICs by optimizing the glass production conditions.