I wanted to give this an 'informative" "i", but 4 feet per bird is excessive (though more roosting space would be helpful), but 
square feet  of roosting space?? She would need to make the whole coop a platform!!!! ( 

 oh, silly me, that is what the coop floor already is!!)
Seriously, though, 
@RebeccaBoyd  if you can add an additional roost, 
 and on the current roost(s) put up (a?) barriers (sheet/pillow case hung strategically so there is a visual barrier to 'break the roost' into sections might help.
EDIT to add:  Or, even like what 
@BY Bob did in the cluckle hut - a barrier of chicken wire so no pecking through it. - on the roost.  Unfortunately with you, you have multiple hens that are antagonists - not just the one Phyllis, so you will probably need to add a roost (new, and slightly lower than the others, so old girls won't want it but newbies will have a space), plus put up 'barriers' on each of the current 2 roosts - that might give them enough places (5 ) to find a roost and not have the bullies harass them - especially if they learn to roost a bit later, once the bigs are settled and it is dark enough they may not switch roosts to harass.