Microsoft requires a mobile number when setting up Windows 10 Build 17063

If you want to finish installing the latest version of Windows 10 pro product key Build 17063 from Microsoft, you must provide your mobile number to the company.
According to PhoneArena, the screen asking for the phone number will display "Link your Phone and PC. Windows product key loves all your devices-get essential apps that help you work better across your devices.
You will not see the Skip button to ignore the request, and when entering a cell phone number, an SMS message will be sent to the smartphone to link the two devices. This allows you to use features like Continue on PC, which is an application that allows you to continue accessing a website on your phone and complete it on your computer screen.

Previous versions allowed Windows 10 users to skip this action if they wanted to. When it's displayed, they just click the Skip button, but that does not exist in the new build, meaning they can not ignore it.
Most likely, Microsoft office 2016 product key just wants to get your phone number to promote its dedicated app. Of course, in case of receiving a lot of reaction from the consumer, the company can return this button.