Why does matter change from one phase to another

the state of matter depends on its temperature and pressure. example, at constant pressure of 1atm (atmospheric pressure), water at 100 degrees Celsius is vapor, and at different phases at different temperature. Note that's at pressure other than 1atm, water will not boil (be vaporized) at 100 degrees Celsius, it could be lesser or higher (depending on whether pressure is increased or decreased).

Therefore, the state of mater changes with respect to temperature and pressure action on it.