Leader ability sidious or Phasma ?

Here is the thing about Phasma. If you are using Sid and Kylo you have a chance, if they are called upon, to add a healing debuff to the target. If Dooku is called he can proc a stun (same with Daka). So overall Sid might look like he is better, but Phasma outperforms because of the lockdown characters can do on their normal attack. And don't forget about TIE Pilot.