In Google’s official blog, Google announced an update to the mobile-friendly algorithm in May:
Today we’re announcing that beginning in May, we’ll start rolling out an update to mobile search results that increases the effect of the ranking signal to help our users find even more pages that are relevant and mobile-friendly.
If you’ve already made your site mobile-friendly, you will not be impacted by this update. If you need support with your mobile-friendly site, we recommend checking out the Mobile-Friendly Test and theWebmaster Mobile Guide, both of which provide guidance on how to improve your mobile site. And remember, the intent of the search query is still a very strong signal — so even if a page with high quality content is not mobile-friendly, it could still rank well if it has great, relevant content.