You know man, I hate to say it as i like my all my snakes a lot too but it might be time to cut Phyllis loose. I mean you have tried everything under the sun with no improvement other than keeping her in a food coma which isnt going to be good for her.
I personally dont think a bigger cage is going to do it and spending all the cash to build one and find out it didnt work is REALLY going to be aggravating. It might be Phyllis doesnt like AP cages as that is the only thing left but personally i cant see that being it.
I honestly have run out of ideas to offer. Maybe look for a smaller cage from a different manufacturer for cheap on CL or something and try that. If it works, then maybe build the monster cage and resell the smaller one from CL or give it to the boa.
Sorry for all the problems. I know what it likes when Caesar was going crazy during breeding season and pushing his face into hamburger
