The phantom hit does no base damage on its own (it didn't when it was on Sated Devourer either), just duplicates what on-hit effects you have. Because of the lack of base damage, lifesteal won't proc unless you have an on-hit effect that is effected by life steal, like Blade of the Ruined King or Ravenous Hydra.
Jinx rockets are bugged with it; apparently, the 10% bonus damage was supposed to be able to proc on Phantom Hit doesn't.
Varus's W has base on-hit magic damage that is effected by rageblade, as well as having massive attack speed from his passive.
Rageblade applies things like the on-hit from Kog Maw's W or Kai'Sa's passive on-hit damage, and things that stack on-hit like Vayne's Silver Bolts or Kai'Sa's Caustic Wounds stack faster with phantom hit.
It used to stack Caitlyn's headshot faster, but this interaction was removed as a result of the removal of her Headshot's interaction with Runaan's Hurricane.
These are just a few examples of what Phantom Hit applies, as far as marksmen are concerned.