Why Does the Temperature Remain Constant During a Phase Change from E to F

Temperature remains constant during phase change because at that point, any energy added to the substance is used to change its phase rather than to change the temperature. In other words, during phase change, the distance between the molecules changes, but not the translational velocity of such molecules or particles.

Why does the temperature remain constant during the phase changes?

During a change of the state of matter, the supplied energy is not used to increase the kinetic energy of the molecules, but to change the binding energies. Therefore, the temperature remains constant.

Why does the temperature not change during phase changes?

But there is no temperature change until a phase change is complete. i.e. during phase change, the energy supplied is used only to separate the molecules ; no part of it is used to increase the kinetic energy of the molecules. So its temperature will not rise, since kinetic energy of molecules remains the same.