It is, but Apple seems to have become the largest customer and Foxconn's revenue seems to rise and fall with Apple's iPhone sales. This article [1] from 2013 states that "Hon Hai [...] draws an estimated 60 to 70 percent of its revenue from assembling gadgets and other work for Apple Inc.".

[1] http://www.businessinsider.com/apple-moving-from-foxconn-to-...