There is one set of Google search results for desktop size screens and another set of Google search results for mobile size screens. Without a mobile responsive website you would be missing out on all the searches people initiate from their mobile (which is the biggest majority). Google now rates “mobile responsive” as the main search result ahead of desktop versions.
To tell if your current website is mobile responsive, here is Google’s free checking tool www.google.com.au/webmasters/tools/mobile-friendly/ enter in your url and Google will evaluate it for you