This issue doesn't appear to be affecting Windows Phone devices when they search directly in their Bing app. It also doesn't appear to be affecting image, video or news search results. Hopefully Microsoft will fix this problem ASAP and when they do we will provide an update.
Update Looks like search results on Bing are back to normal. The outage seemed to last an hour or so on our end.
Update 2: Microsoft sent us this statement about the outage: ""Microsoft became aware of an issue earlier this morning causing some users to experience intermittent access to Bing. We took immediate action and restored access to the service."
Thanks to the many folks who tipped us!