In a move to be able to better support devices in the future with updates, Google has moved their stock Contacts and Phone apps to the Play Store for updates. Google has already done this for apps like Calendar and others, so this is nothing new.
However, there are a few caveats to this change. For now, these apps will only work on Nexus, Google Play Edition and Android One phones and tablets running Android 6.0 Marshmallow. Hopefully Google adds support for other devices, as more devices have been getting Marshmallow lately.