So Phase Rush currently isn't being taken all that much, with some champs like Viktor even opting into Fleet Footwork. My idea to make it more a more attractive option is:
Basic attacks and abilities generate stacks on enemy champions hit, up to one per attack or cast. Applying 2 stacks to a target within 2 seconds grants 30% - 50% movement speed (scaling with level) for 2 seconds (20% - 40% for Ranged users). Once proc'd, if an additional stack is applied within 2 seconds the movement speed buff is extended by 2 seconds and the user gains 70% slow resistance (50% for Ranged users) for the remaining duration of Phase Rush. 15 Second CD.
This makes it much easier to proc and integrate into trading patterns while rewarding users that stay in the fight. The Ranged nerf of course doesn't have to be there but the 2 ability/auto proc may make it hard for melee champs to trade back in lane so I put it in there. Let me know what you think!