Apple has returned at least 5 million iPhones to Foxconn due to substandard appearance or dysfunctional problems, according to a new report out of China. An anonymous source said the number of rejected iPhones could be as high as 8 million. It’s estimated the issues could cost Foxconn as much as $1.6 billion to cover the cost of replacement handsets. The report didn’t specify which iPhone model failed Apple’s quality tests. [via…