I had time to some of observe this.. and i think im gonna answer my own question o.O haha XD
I tested it in practice mode
as you can see in the pic the damage of lvl 1 PR is stronger than the damage of lvl 2 PR
i think both of them are hard to counter.. i haven't tested lvl 2 in pvp yet because all of my skills for sieghart are LVL1 because most of lvl1 skills are uncounterable or hard to counter..
and for me when i'm testing it on practice mode.. phantom rush Lvl 1 has faster execution than LVL2..
haha it feels weird.. answering my own question...