In other categories it is possible to 3 cycle him instead of the 4 cycle method below and still without any RNG of waiting for Zant. To do this stab him then do 2 quickspins, repeat this for the 2nd cycle and for the final cycle do 1 slash then 3 quickspins to finish.
This strategy may not be perfect in theory however it eliminates all RNG from the fight and hence is best strategy. It does require you to be able to hear and locate Phantom Zant fast. The idea is that Zant doesn't teleport around the room until he spawns his first wave enemies, and if you don't deliver the final hit of the combo he won't start spawning enemies. Because of this we can stop him ever teleporting around the room by just doing 3 stabs for 3 cycles and then on the 4th cycle deliver the combo which will kill him.
In 100% With Fixed EMS you should have greatspin at this point and if you do you can 1 cycle both Phantom Zants. To do this simply stab him once then do 3 greatspins. If you only get 2 greatspins, you can just combo him next time round. If you only get 1 greatspin then next time do 3 slashes and a greatspin. The window is very wide hence 3 greatspins isn't hard.