Just let it be. Eventually it'll drop when it's ready, in the meantime the green part continues to photosynthesize and nourish the plant. Your house is on the cool side for a Phal - it won't be damaged but may grow only slowly. As far as roots are concerned, I don't recall when you said that you last potted it. If it was recent (less than 6-8 months ago) don't disturb it - if it needs to grow more roots, it needs to be left alone to do that.