I recently learned how to upload video captures from my Xbone to YouTube. Pretty fun stuff to play around with. Here is Nisha bypassing the 3 phases of DSR. The build I typically use is a variation of @charrisx build. Enjoy…
What is the key to bypass the phase change ?
Seems like when I do this damage stops registering.
Same. I’ve had a shock Rosie and housed the shield and the first third of the bar and then damage stops registering.
Luck and killing him before the stun lock animation is over in my experience.
So, it’s the same as with EOS ?
With EOS you have to kill the last 80% of his health in less than a ~1/5 of a second.
Not knowing the technicality of why this can be done will inhibit my response. But in a nutshell, yes. It’s kind of like EOS. You just have to put out enough damage quick enough to bypass the phases. I have only been able to do this with Nisha. All I do is get a kill before I concentrate on DSR. I focus on a tenticle first. After the tenticle is dead I immediately jump into showdown to focus all damage on DSR. I can only accomplish this solo for obvious reasons. 
@Chuck80 Maybe my fingers are quicker than I give them credit for. 
@Chuck80 and @khimerakiller, So I attempted to recreate this vid for you two displaying what’s under the hood so-to-speak.
I made 3 attempts over the weekend. I was successful 2 out of 3 times. Here is the 1st run…which I admit I was lucky.
This is the 3rd run and went much smoother…
You can kill the bug in the chest for an easy kill skill.
Pro tip 
it’s amazing how some tips are so simple it’s genius. To think I never thought of that is just mind numbing…
Thanks @khimerakiller. Great tip. I have a vid of me running around with a yellow glitch using the melee to stop the yellow loop prematurely. Thanks for that tip as well. 
Correction. I have recently accomplished this with a coop buddy in game. So, it doesn’t have to be solo. 