Doctor Phlox is a fictional character in the television series Star Trek: Enterprise played by John Billingsley. Phlox is the doctor aboard the NX-01 Enterprise.

He is a member of the Denobulan race and was on Earth as part of the Interspecies Medical Exchange when called to service on Enterprise. As part of the Exchange, he corresponds regularly with his human counterpart on Denobula, Dr. Lucas.

The doctor is portrayed as having an open mind to any other species and culture and is always curious about certain human habits. His sickbay contains an interplanetary zoo of animals, some of them as food for other animals which are used as source for medical drugs. He has a wry sense of humor. He also has an affinity for Earth cuisine, particularly Chinese Food.

Phlox is also interested in religion - he once prayed with a group of monks which visited the Enterprise, and even attended Mass at St. Peter's Basilica in Rome.

Phlox's physical abilities have been revealed gradually over time. He appears to need little sleep, instead embarking on an annual "hibernation" of sorts that lasts for several days. He also has great control over his facial muscles, being able to open his mouth wider than humans (this has been demonstrated by the impossibly large grin he occasionally sports). When confronted with loneliness, his people can sometimes create incredibly realistic hallucinations. When threatened, Phlox also has the ability to inflate his head like a blowfish to scare off predators.

In the Mirror Universe, Phlox is not the engaging, peaceful and friendly character he is in the normal Trek universe. The mirror Phlox dresses in a severe black leather uniform, unlike the civilian clothing worn by his counterpart. Mirror Phlox resembles Josef Mengele in his utter lack of morals - he routinely experiments on living beings in horrible fashion, in his sickbay which resembles a chamber of horrors.