No, it's true. They bounced around the idea of Tony singing silver rainbow and Mike singing just a job to do. I read Tony's comments on the matter and that they decided in the end that Phil was the best singer so it didn't make sense. However, can I remember where I read that? No. Can I link to material supporting the claim? Also... No. I came across it many years ago in a book, or magazine. Or it might even have been a recorded interview as I can remember the comments in Tony's voice.
Well in the end I am happy that Phil sang the songs...