Microsoft has confirmed that the new EdgeHTML.dll rendering engine for Internet Explorer is being used in the newly launched Windows 10 techical preview for phones. The new engine is already being used in the Windows 10 preview for desktops.
The company also went over some of the other features that have been put into this first Windows 10 for phones preview release in terms of its support of web platforms:
The new web browser that Microsoft is currently working on, under the code name Project Spartan, is not part of this first Windows 10 preview for phones. However, it will use the same rendering engine that IE currently has in this build. Project Spartan will replace IE entirely in a future preview build of Windows 10 for phones.