Different glasses suitable for temperature sensing in the fiber optic sensors were studied in this article. The phase changes for eight different glass materials were calculated and results were compared. Our results showed that extra dense flint glass is the most sensitive one, while pure silica results in the lowest phase change. In another study the effect of wavelength on the phase variation was also investigated and the results were presented. Finally, the effect of glass formation in phase change was considered for different glasses, which were prepared using different techniques. The result showed that the Corning glass #7940 offers the highest sensitivity in comparison with the other three glasses for temperature sensing. Our studies for different silica glasses indicated that glass formation is important in preparing the glass materials required for the fiber sensors.