Haven’t filled out all of your timeline information? Your Facebook friends can ask you to do so. Some users are seeing prompts on mobile and desktop to ask their friends for information that isn’t present on timeline, such as phone number or address.
When a user visits the “About” section of the desktop or mobile timeline, they’ll see a prompt that will allow them to ask their friend (this only works for users with whom people are connected) for information.
Users can then send a note, explaining to their friend why they’re asking for this information:
Source: Inside Facebook
Facebook prompts users to ask friends for key timeline data