It depends on the type of pheasant. Some are monogamous, others run in trios. Not that I'm any kind of pheasant expert.
However I do know that if you take birds from a cage bred environment and just release them into the wild, many if not all would fail to survive. They need to have been raised in a fairly natural environment for that, to have the instinct and ability to cope. Some pheasants have been domesticated for countless generations and would probably do about as well as any cage bird if just released into the wild without prior training and 'rehabilitation'.
Being afraid of humans is no indication that they have the rest of their wild instincts intact. If they haven't been able to act on these instincts over even a good handful of recent ancestral generations, then there's every chance those instincts are flawed at best, lost at worst. If they're not native to your locale there's another risk, that of them eating toxic plants and insects for lack of knowledge of safe feeds.