There are several ways, depending on how many parameters are involved and what happens behind the scenes.
Probably the easiest and most practical way is to let your existing php script take care of it. Before the php starts processing the request, let it look at the parameters. If they're in the wrong order, put them in the right order and issue a redirect. Your php is a lot more flexible than mod_rewrite and can do more complicated calculating and rearranging.
That's assuming it is your own php, not an out-of-the-box CMS that you can't edit. Otherwise it is back to mod_rewrite. Or over to a separate php script which you do write yourself.