I had a really good experience the last mental health trip we made to the ER. It all depends on where you live and what else is going on that night, but if he is scared that could be the best and safest option.
I agree that he needs medical attention. Psychosis and it could become worse. My heart goes out to you.
I don't know enough about your medical system. But some one hearing voices and has history would be admired to psychiatric ICU for observation.
It depends on how safe he feels. What about you going to him and assessing the situation first hand rather than over the phone? Do you have a county mental health service that you can call for assistance?
Yes. A regular ER. Depending on where you live, they might not keep him though if he isn't dangerous. In our city, there is a mental health check that you can request by calling 911. You might try that.