Starting April 21, we will be expanding our use of mobile-friendliness as a ranking signal. This change will affect mobile searches in all languages worldwide and will have a significant impact in our search results. Google
Most newer and high quality themes and templates for the likes of WordPress, Shopify and Weebly are responsive which means that are already mobile optimized. If you’re unsure if Google sees your website as mobile optimized then use the free Mobile-Friendly test by Google.