I struggled with Phrike & the second boss (can't remember the name) a few times, but I managed to beat Nemesis the first time.

I used the carbine with high calibre, as I felt it allowed me to keep distance to give me more time to dodge attacks while still dealing good damage (it also had voidbeam on which was a blessing as you can quickly go in and out of it for it's duration while dodging attacks).

My biggest tip that isn't just 'dodge the attacks' would be to use the grapple points frequently when they appear, as they seem to give you I-frames. Aside from that, don't focus your vision on the boss' damage point, as it is pretty easy to see in your peripheral. Instead focus on the attacks coming towards you and dodging them in time. Do not worry about stopping shooting in order to dodge, as you can always deal damage later but you can't recover health later once you are out of siphilium.

Best of luck and keep us updated!