While Grace Phipps is a talented actress, she does not sing in the show. The singing in "Fame" is primarily performed by the other cast members, especially Collins Pennie (who played the character Tyler) and Chloe Bridges (who played Daisy).
It's a common misconception because of Grace Phipps's strong presence and the character's involvement in the school's musical performances. However, her singing voice is not featured in the series.