To be honest, i'm clueless as to how to fight the Pahlava. I've been attacking them in towns where their horses don't have the mobility of a field battle, and then defending towns. I've been waging war in city streets rather than out in the open, because i know if i go out in the open i'll be quickly annihlated and lose some very important eastern provinces which generate a lot of income for me.
You answer yourself :-)

and one more thing, use your elites as soon as possible I have no idea but I can only kill an elite AS Phalanx around %10 but can easily kill medium ones while playing with pahlava.

I think while they are in phalanx mode they have a defence bonus against arrow attacks.