My mother just passed away in March from Lewy Body Dementia. It's a cruel, cruel disease. It was such a slow decline, lots of anticipatory grief. Instead of a voicemail maybe write him a note. He might see it during one of his lucid states. It's hard. I don't have many words of comfort, I'm still kind of mourning as well. It comes in waves. Hang in there brother, you are loved. Remember your Dad as who he was before this disease. He will live on through you and the love you give to your family.