I only play with japanese audio too so I don’t know what line to listen for, I just try to look for visual clues but it would be nice to know what line it was.
I cannot speak Japanese so correct me if I am wrong. When I hear Amani (JP voice) I activate phantom time then use finisher, and it works every time, and the time window is quite wide, you have 3+ sec to respond to it.
You can hear almost the whole phrase, see her float a bit, point her sword upward, rise a shield and if you hit her after all this, you get frozen. There are many many many signs to notice it, I only got hit when I was reading messages on my second montior when fighting or when I accidentally luster stepped.