Is there a calm or slow hen you can bring in with Phyllis? I ended up with something similar, minus the roos. One of my hens, Phoebe, got pecked, stripped, plucked to where her side was bloody -- she was even pecking herself. So I separated her out till she could heal... but then I couldn't get her back in with the flock. I'm not sure which came first -- if they chased her or if she screamed and caused them to chase her to shut her up. I do know that having a house chicken was a huge mess! Even keeping her confined to the kitchen was a mess with cleaning up poop blobs constantly.
As luck would have it Marilla injured her leg -- she could not chase anybody. So I put her in with Phoebe and they are now fast friends.
My next step is to put them both in the same run with the others, but divided with chicken wire so they can see one another, but not grab one another. I'm going to do this for an hour or so every day till eventually I can put them together supervised for a short periods of time till everybody's friendly.
It's a lot of work... but it sure beats the mess of a house chicken.
Good luck with yours -- I know you will come up with a plan that will work for you and for Poor Phyllis. (Another choice would be to pair her with a friend and give them to a 4-H kid.)
Jenny