If you have a responsive website - meaning your site works in all screen sizes - then yep - you're groovy. If you have a old-fashioned mobile friendly site that some newspaper gave you for free when you bought an ad in the paper - you're compliant. Not groovy tho. Most users do not like mobile sites - they feel like they are missing something from the full, main site. Surveys say only about 5% of everyone like mobile sites.
Responsive websites work in all screen sizes, from desktop to smart phone, without having to adjust sizing to read words or see photos. There is one site to maintain, and it flows 'responsively' to the size of the screen based on content priority. This is a must have. Among the various algorithms of Google, the lack of a mobile friendly site doesn't just get you a bad grade, you are penalized.
This would be a -we need to fix this right now- kind of emergency.