The Phobis devices were mysterious Sith artifacts that harnessed the power of fear with only mere exposure to them. They were filled with dark energy that left all but the bravest of minds crippled with horror. Three such machines were created, and the Sith Emperor was known to have sealed the Core component within the Dark Temple where it remained active and likely spread fear and hysteria for generations. Many Sith had meditated on these machines to learn their secrets but were driven mad as a result. The only beings who had managed to learn their power were the Dread Masters. They successfully harnessed and perfected the Phobis devices' terrible power by using it against the Republic.
It was also said that if one were to merely bask in the presence of one of these devices, the device's sorcery would force the individual to live all of their greatest fears within their mind until either the individual were to face these fears, or be driven mad.
- Star Wars: The Old Republic (First appearance)