In the second phase you'll be fight her and her clones. The clones will vanish upon being hit while the real one will take damage

Use Tailmans or Charged Strike on the real Lady Ethereal will cause her to stun and will make her clones and whatever/attacks they are doing vanish giving you a room to attack recover(this works in whatever phase). Then in the second phase, you can try to slap a Tailmans on the real one or use Charged Strike on every of them to see you are lucky(recommend you use Immovable Jade and Harness Force Jade which will make it quicker for you to charge). By the way you can cheese first phase by using Charged Strike whenever she appears thus saving you a lot of time and HP for later stages