Phyllis reveals to Bill during their prison conversation that she knows about his affair with Ruth, though it sounds like she could also be referring to his affair with Betty, his assistant. Perhaps Bill has been a busy boy having multiple affairs — it sure sounds like that's the case with Phyllis. She's been having an affair with their lawyer, George Bautzer, and possibly someone else. She tells Bill he's going to jail for life for killing Ruth, but she says it in more of an "I framed you for this" way and not an "I think you're guilty and you should pay" way.
So maybe Phyllis got tired of her marriage and decided to kill Ruth and frame her husband for it. That definitely feels likely, though that's a big job for her to pull off by herself. We think she probably had help in the form of . . .
