How do you approach a patient request to decrease hemodialysis time when Kt/V values are above target but serum phosphorus remains poorly controlled?  

Reducing time is the wrong approach, phosphorus control is a long-term problem and we all know it will go up and down. I only accept time reduction when approaching end of life to make the patient more comfortable. By then, I would have already started palliative care conversations.

I would explain it to the patient why it is the case that longer dialysis may be helpful. Then, I would make a deal with them that if they are able to control their phosphorus for 3 months in a row, I would lower their time by 15 minutes and go from there.