Google started its mobile-first search indexing over a year ago, and now it's ready to make that approach the law of the land. As of July 1st, 2019, Google will index the phone-oriented sites by default for any new web domain it registers. If you're starting a new site, you'll want to be sure its mobile version is polished and full-featured -- that's the version Google will use to parse the site's structure and extract useful snippets.
The strategy has been a long time in coming. Google first signaled its intentions in late 2016, and it wasn't until early 2018 that it was active for more than a handful of sites. And remember, mobile searches overtook their desktop counterparts back in 2015. This is as much about catching up to the reality of a mobile-dominated web as it is persuading web developers to give phones a first-class experience.