Every version of Harry Potter and the Order of the Phoenix — the books & films, compared across media.
Voldemort has returned, but few in the wizarding world will admit it. Harry Potter and the Order of the Phoenix follows Harry after a Dementor attack on his cousin, as a secret order gathers at Grimmauld Place and a new Hogwarts professor leaves students unprepared to face the rising threat. J.K. Rowling's 2003 novel and the 2007 film adaptation tell this same story across two media, each reaching the material in its own way.
Yes. The 2007 film adapts J.K. Rowling's 2003 novel Harry Potter and the Order of the Phoenix, in which Harry faces a Dementor attack and discovers a secret order forming against Voldemort.
There are two: the 2003 novel Harry Potter and the Order of the Phoenix by J.K. Rowling and the 2007 film of the same name.
The 2003 novel follows Harry's fifth year in full, including the secret order gathering at Grimmauld Place; the 2007 film centres on Harry training students to defend against the dark arts when Hogwarts leadership falls short. Which to choose depends on how much depth you want.