Microsoft to call Windows Phone replacement Windows 10 Mobile

"Windows 10 Mobile is designed to deliver the best user experience on smaller, mobile, touch-centric devices like smartphones and small tablets. It boasts the same, new universal Windows apps that are included in Windows 10 Home, as well as the new touch-optimized version of Office. Windows 10 Mobile offers great productivity, security and management capabilities for customers who use their personal devices at work. In addition, Windows 10 Mobile will enable some new devices to take advantage of Continuum for phone, so people can use their phone like a PC when connected to a larger screen."-Microsoft
Microsoft says that Windows 10 will be released this summer, although we don't expect to see Windows 10 Mobile arrive until the fall.
source: Microsoft via TheVerge, MobileSyrup