There is an old Chinese saying: A holy bird(凤凰) flies out of a remote, undeveloped mountain area, which means a man who was born in a poor family becomes successful (often rich) later.
But “凤凰男” is a newly coined term, which hints a successful man with a poor family background usually can't get rid of the bad habits and backward ideologies brought from his background, and when he marries a girl from a better family background, conflictions will arise.