If we measure success in terms of market share, Windows Phone was registering in the single digits as of January 2014. This is 4 years after the original WP7 released. So under 10% in 4 years is not a rousing success.
Financially success is probably not assured given such low market share. MS has not separated out their earnings and profits for Phone except recently: Q4 2014
Phone Hardware revenue was $2.0 billion, reflecting sales of Lumia Smartphones and other non-Lumia phones following the acquisition of NDS on April 25, 2014. Since the acquisition, we sold 5.8 million Lumia Smartphones and 30.3 million non-Lumia phones.
Phone Hardware gross margin was $54 million, reflecting revenue of $2.0 billion, offset in part by $1.9 billion cost of revenue, including amortization of acquired intangible assets and the impact of decisions to rationalize our device portfolio.
So gross margin is 0.054B / 2.0 B = 2.7% overall for phone. Note this is for all phones not just Windows Phone; however sales were only 5.8M. Financially that's terrible performance. If you compare it so Apple (and people will): 35M, $19B, (no margin reported).