Microsoft's phone business fell off a cliff, sales for the Lumia were down 73%

Microsoft only sold 2.3 million Lumia phones last quarter. That's a massive 73% drop from the same quarter last year, when the company sold 8.6 million phones.

In documents filed with the SEC, Microsoft explains that this whopping decrease in phone sales is due to "the previously announced change in strategy for the phone business."

That strategy was to lay off most of Nokia's employees and write down nearly the entire value of the acquisition and start building first-class apps for Android and iPhone instead.

And the lack of focus on Windows phones is having a ripple effect. Sales of phones by other makers, like HTC and Samsung, were down by 36%, too.

Here's how Microsoft explained its phone business when it reported its Q3 fiscal 2016 on Thursday (emphasis ours):

Devices revenue decreased $248 million or 11%, driven by the previously announced change in strategy for the phone business, offset in part by higher Surface revenue. Phone revenue decreased $662 million or 47%, as we sold 2.3 million Lumia phones and 15.7 million other phones in the third quarter of fiscal year 2016, compared with 8.6 million and 24.7 million sold, respectively, in the prior year.