You mean like Boba Fett in Empire?
Yeah that's a possibility, but Boba still played a fairly important role in the story, as the bounty hunter who tracked the Falcon to Bespin and flew off with the captured Han at the end.
It's still not clear if Phasma will be nearly as important, or if she'll just be a glorified henchwoman who leads some troops around and reports to Kylo Ren now and then. Hopefully we'll at least get to see her in some one-on-one combat with somebody, or she'll be one of the characters surviving to the next movie...