Parent poster is probably conflating Windows CE, Windows Mobile, and Windows Phone.

Windows Mobile 5 was tremendously popular with over 100 phones from various manufacturers. But that was also around the time iPhone was released and by the time Windows Mobile 6 rolled out, the iPhone 3G/3GS was taking the world by storm. Windows Mobile 6.5 had a partially revamped UI but not enough to be competitive. From there we go to Windows Phone 7, 8, and 10 and that story is well known.