Modified Phase Shift

Hi all!
I'm trying to make a sort of custom phase shift ability.
Basically, when a unit is attacked it should be able to 'dodge' this attack by activating the custom phase shift (an autocast ability).
However i'm having difficulty with this for the following reasons:
I don't think phase shift stops the damage which was the reason for phase shifting - only the damage that would be taken *while* being phase shifted.
Also, the unit must be able to attack at its normal attack rate (i.e. the unit must not have its attacks interrupted even if phase shift has triggered, so i guess i might need a variable length phase shift)
Clearly this might require triggers, but i'm just wondering if anyone had some suggestions for how this might be achieved, or if i'm going about this completely wrong?

Thanks in advance

If you want it to be autocast, you'll have to trigger the autocast, BUT you could use a modified berserk to reduce damage taken for a very short period by a factor of -1.