His singing is layered in with, at least, Freddie Mercury’s own voice, and likely Rami Malek’s as well, to create something a little different so we’re not simply listening to prerecorded lyrics from Queen albums.
Martel’s voice also isn’t heard alone.
Martel doesn’t specify exactly which songs in the movie he performed, and he’s very clear that he is only “one of” the voices of Freddie Mercury that we hear in Bohemian Rhapsody, though he admits he doesn’t know who else may have contributed.