Microsoft, like any company, loves money. The best way to get said money is to make sure your products are on as many devices as possible, especially when those devices are selling loads more than your own platform.
Nikkei (via Reuters) reports that Microsoft will be bringing its popular game franchises to iOS and Android devices later this year. The company will be working with third-party developer KLab to bring its games to competing devices.
The first game is a free-to-play Age of Empires title. It's unknown if it will be a mobile port of the recently released PC free-to-play Age of Empires title, or an entirely new entry. Microsoft would only tell Polygon that it's a "mobile version of Microsoft Studio's Age of Empires franchise."
Of course, Microsoft isn't leaving Windows Phone out to dry. After an initial launch on iOS and Android, the mobile Age of Empires will be released for Windows Phone as well.
The original report mentioned that Microsoft would be bringing more of its franchises to Android and iOS, but a statement from Microsoft says that "there are no further announcements beyond Age of Empires at this time." It may be a bit disappointing for those hoping for a mobile Halo or Fable title, but Microsoft's statement doesn't rule out the possibility. In fact, it's pretty likely that Microsoft will continue to invest in mobile games. There's already a precedent with Microsoft developing a port of Kinectimals for mobile as well as a number of Xbox companion apps.
Speaking of which, might I suggest that Microsoft port Halo: Spartan Assault to iOS and Android. It can then tie it into Halo 4 and any other future Halo titles through Smartglass. It's pretty much guaranteed that a mobile Halo title would do better on iOS and Android then on Windows Phone 8.