Google is introducing a new Mobile-first Indexing. This change supposed to address an issue where the desktop and mobile versions of a page vary in content and markup. Up until now, when users search on Google using a phone or any mobile device the ranking system would most likely utilize desktop version of a page’s content. With this new indexing this should no longer be the case.
While so far this is a limited and experimental change in indexing, it is a big development and Google urges users whose websites are not responsive or dynamic serving and where content and markup varies between mobile and desktop version to consider following:
Make sure to serve structured markup for both the desktop and mobile version. Sites can verify the equivalence of their structured markup across desktop and mobile by typing the URLs of both versions into the Structured Data Testing Tool and comparing the output. When adding structured data to a mobile site, avoid adding large amounts of markup that isn’t relevant to the specific information content of each document.
Use the robots.txt testing tool to verify that your mobile version is accessible to Googlebot.
Sites do not have to make changes to their canonical links; we’ll continue to use these links as guides to serve the appropriate results to a user searching on desktop or mobile.
If you are a site owner who has only verified their desktop site in Search Console, please add and verify your mobile version.
Also to confirm, if you only have a desktop version of a website or you have responsive site where content and markup are the same across, you should not need to take any actions.