Tips For Citadel Des Morts Boss Fight

I faced the boss 4 times now twice as a solo and twice as a squad of 4 and all 4 times there is no issue getting to the last phase but as soon as it progresses to the final stage I just get slapped.

I'm aware that you can parry stomps and swords are the way to go but never seems to go well for me.

Any advice is appreciated.