Phase Rush is Almost a Troll Pick for Melees
The %75 slow resistance was unique to melees but it got changed to be available for all but even those times phase rush saw low to no play. Then it got changed to start from %25 instead of %40. Who is using it? Bruisers prefer conqueror, tanks prefer aftershock or grasp, assassins prefer electrocute, some of them dark harvest.
Let's remember why the new rune system happened. It changed runes so it could be open to a more open variety of champions. We lost Stormraider's Surge to get this because some champions who would want to use it couldn't afford the %30 damage threshold. So it got released with that nerfed %15-%40 version. Got buffed to %25-%40, ranged champs now have %75 slow resist too. No melee uses phase rush because taking it just means you won't win nor escape from any damage they deal back to you in lane trades. Not even mentioning cooldown going from 10 to 15. Again this is alright for mages. Why for melees? You already lose all the combat potential you had as I said, while gaining so little.
What I'd just say give it back the %40 movement speed for melees, only on ranged champions make it scale. Or just make the slow resist scale and not begin from %75? I just want to use this rune like Stormraider's again...
Take a look Riot won't ya?
but even that is a rare occasion and EVEN THEN it rarely helps a lot. You are just simply better off taking conqueror.