Phantom High is a Manga/Manhwa/Manhua in english language, Manhwa series, english chapters have been translated and you can read them here. You are reading chapters on www.mgeko.cc fastest updating comic site. The Summary is

Don't let them find out you're human! Ingan Kim, a normal human man, suffers an unfortunate fate of having to work as a teacher in Hell's Phantom High, where spirits and monsters are students. His only chance at survival is an elixir he uses to hide his human scent. If his students ever find out that he is human, he will be done for. Everyday, he asks himself: will I be able to keep my human scent hidden from these students who will eat me up?