Matalas was a planet where Doctor Phlox was once nearly overwhelmed by fifty patients in a refugee camp.
In 2151, Phlox recalled this event to Dr. Jeremy Lucas in a correspondence, while relaying the incident in which Enterprise NX-01 encountered a pair of astronauts from Valakis. (ENT: "Dear Doctor")
This planet was only mentioned in dialogue.
The event might be set in the unidentified war in which Phlox served.