Windows Phone’s biggest contribution to the hi-tech industry will be as a proving ground for some of the more distinctive features of Windows 10, such as the user interface and the Cortana virtual assistant. But you wouldn’t have known that from Microsoft’s Build developer event this week, at which its mobile operating system, and indeed smartphones in general, got scarcely a mention. It is fair enough for Microsoft to concentrate its initial W10 efforts, as Windows chief Terry Myerson explained, on its more established developer communities outside the mobile world where it has consistently failed to get established. But that does raise question marks over its whole mobile strategy, at a time when more and more computing and media activity…