Mass of Ice during Phase Change
When the temperature of the ice has reached 0°C, additional heat transferred from the liquid water to the ice will not increase the temperature of the ice above 0°C. Instead the transferred heat is consumed as heat of fusion. This lets ice melt, which means that there is a phase change from solid to liquid, which means that a certain mass of the ice is transferred to the liquid water. The mass of the ice consequently decreases during the phase change.