I haven't been sleeping for almost 3 weeks in-game now. However, no phantoms are spawning and difficulty is set to hard, there are blocks on top of my head, I'm above level 63, and mobspawning is set to true. My other friend has the same problem. At first, I thought I might have been sleeping too much but then my friend said it happened to them too so I had to report it. Once, a phantom did spawn when my brother and I were playing split-screen, but that was the only time and it was only one phantom. It never happened again.