SPOILER:
for anyone wondering I figured out the parasites second phase pattern:
first top middle.
top left
top right
then to your position.
top right again.
then twice to your position.
and repeat.
so best chance to attack with swarm once the parasite starts the 3 fixed position attacks.
or, if youa re quick enough, when it does the singular top right attack.
but keep in mind that the grounded swarm takes a while and a position based attack might come before you can move away.
Also, for first phase, i just stood in the bottom right corner, waited for the spike pattern to show and like a second or so later moved a bit to the top left. and hit with swrm knife to the right when the ghost was miving up again. about 4 damge each hit. gets easy to do without taking much or any damge once you got the rythm down.