It took me a while to think of someone but I think Martin Freeman fits well. Mostly unfazed by scary things but still jumpy and cowardly. In those moments he uses intimidation though, the enemy sees something very different, almost demonic. When the phantom resides in my characters consciousness, it provides Skill Focus Intimidate. As fluff that is going to appear as a psychic projection to make him seem more terrifying. He uses his powers to make them see, like, burning eyes, no eyes, horns, fangs, whatever the opponent finds frightful or unnerving.
Also, manifestation will be to new to him. Whatever happens to their minds lowers his control and the nightmares gain some new powers. So each time it manifests, the phantom will look different based on what he feared as a child or the new horrors presented in the module.