The American Idol star auditioned to play bride-to-be Tracy Billings in the 2009 comedy but McPhee admits the test failed to win over director Todd Phillips - and the role went to former model Sasha Barrese.
She tells People.com, "It was between me and the girl who got it... I didn't get it, but I went all the way. I would have loved to play that part."
However, the 27 year old, who now stars in U.S. TV hit Smash, didn't hold a grudge - she went to see the movie with her pals once it was released.
She adds, "It was so much better than I would have ever thought it could be. It was unbelievably hysterical, and I remember in the theatre I was like, 'I wish I had gotten that part!'"