Phase Rush needs adjustments
Only 4 champions use phase rush at the very least semi-consistently. Those 4 are Aurelion Sol, Cassiopeia, Darius, and Diana.
Outside of those 4, this keystone is used rarely by anyone else. And even then the rune is pretty underwhelming on Darius and Diana.
It needs buffs or adjustments in its access of power.
Granting bonus move speed just for taking the rune is one way to go about it.
Or granting bonus move speed when approaching an enemy champion is another more interesting change.
One change it could definitely use is granting 1/3 of the bonus move speed before gaining the current full effect at 3 stacks where you gain the max move speed bonus and slow resistance.
. As a midlane or AP focused support, it'd be a really interesting decision between the three Sorcery keystones. It also makes sense in sorcery.