(Reuters) -The owner of the University of Phoenix is targeting a valuation of up to $1.2 billion in its U.S. initial public offering, it said on Tuesday, setting the stage for its stock market return after more than eight years. Existing stockholders of Phoenix Education Partners are seeking up to$140.3 million by offering 4.25 million shares priced between $31 and$33 apiece. Private capital firm Apollo Global is selling 3.55 million shares, while investment firm Vistria Group is offloading 0.7 million ...