Post castration, and the normal discomfort that follows surgery, I'm not aware of any sensation of phantom balls. I have a comparison, I hyper-flexed the great toe on my left toe so severely that it was amputated. That was after the castration but still some years ago. I still feel pain, sometimes acutely, where the toe was. I need to add this. I had the testes removed and artificial ones put in. Some think this means I was never castrated, I disagree but in the context of your question, the fact that I still have a scrotum may deter my nervous symptom from creating false reports.