The veteran producer and movie executive said he was closing the company because "it will be 20 years that the company has been in business."
Phoenix was named for Medavoy's resurrection after having run one of the most successful independent film companies for many years, Orion.
He was involved with such illustrious films of Hollywood's recent history as "Platoon," "Amadeus," "Silence of the Lambs," "Dances with Wolves," "The Terminator" and others.
"Black Swan" was nominated for Best Picture last year, and is one of many Oscar-decorated movies in which Medavoy was a prime mover.
The closing of Phoenix could mark the end of a long-time alliance with his partner Arnie Messer — although Medavoy said he expects he'll continue working with many of his Phoenix colleagues.
"I was at UA (United Artists) for four years. I was an agent for 10 years. I was at Orion I think 16 years, but it may have been 12. I was at TriStar for four years. And now this is the record — 20 years," he said.
Phoenix has a number of movies under way, which will not change ownership. "What to Expect When You're Expecting," currently in production, will be under the Phoenix banner.
But a new project about the rescue of buried Chilean miners in 2010, and a movie version of Ray Bradbury's "Dandelion Wine," won't be Phoenix pictures, he said. They will, however, be Mike Medavoy movies.
"We'll finish whatever is left on Phoenix … Whatever stuff is already in there, we will continue to do. We have a handful of Phoenix projects."
Starting with "The People vs Larry Flynt" in 1996, Phoenix has been production company on 27 movies. It has two films — "What to Expect When You're Expecting" and "Dementer" in production and 13 in development.