Mechanics that rely on RNG or chance/luck are never seen in SC2. Neither attacks or abilities have a chance to do something different (for example, critical strikes or randomized damage or chance based slows do not exist in SC2). 40% chance to avoid an attack is luck based and therefore has no place in Starcraft 2, and even less of a place in a forum RPG.
Even if it were reworked (for example, a variant of the Immortal's hardened shields), it would pack too much utility for a single ability (armor penetration AND damage evasion). I would either rework the damage evasion and eliminate armor penetration or simply eliminate damage evasion and keep it as armor penetration only. With 60 base damage, armor penetration will do little for your hero's DPS as even the most beefy units will have an armor stat less than or equal to 5 (so 8.33% more damage in the best case scenario).
I haven't actually changed Phase Shifter yet. I am letting you decide on how to change it.
Looking forward to your tweaks.