What is Phasma's armor made of?

Phasma's armor in The Force Awakens was made of steel because of the character's last-minute addition to the film. On The Last Jedi, costume designer Michael Kaplan's team had time to plate the costume with silver instead.

Who Killed Captain Phasma?

Following the Hosnian Cataclysm, Phasma was ambushed by FN-2187, alongside the smugglers Han Solo and Chewbacca, at Starkiller Base and was subsequently forced to let down the base's shields, eventually resulting in the base being obliterated.