I'm gonna hatch it to transfer to Pokemon Black
Phione Eggs hatch in 40 Egg cycles.
Generation IV 10455 steps
Generation V/VI 10280 steps
Generation VII 10240 steps
Generation VIII/IX 5120 steps
List of Pokémon by breeding attributes (Bulbapedia) Decreasing Egg cycles (Bulbapedia)
It takes 10,240 steps to hatch it. Good luck!