If phenomena are conditioned, they possess no independent existence and are in flux. If phenomena are always changing, then the fact of their change never changes; their changing nature is unchanging.
If the changing nature of phenomena was not unchanging, then by definition phenomena would not be perpetually changing.
Of course, anything conditioned is by definition perpetually changing. Therefore, if the changing nature of phenomena is unchanging, how do phenomena actually arise and disappear? Why would that which is unchanging give rise to change?