I find the phrase passed, annoying. Passed away, I could just about cope with. What I do know, is that when telling a person that someone has died, one needs to be quite clear so there is no misunderstanding. So I think one of the best ways to say it is to say," I'm sorry to have to tell you, but so and so has died." Not, as I was informed about my father's death that there had been an accident, there hadn't, he had had a heartache and died. Actually my mother didn't even phone me, it was the man who lived in the flat below her. She phoned other people but not me.
It made me ill for months.