The WordPress open-source content management system (CMS) will show warnings in its backend admin panel if the site runs on top of an outdated PHP version.
The short-term plan is to migrate as many active users to more recent versions of PHP as possible so that the WordPress team can drop support for older PHP versions altogether.
The long-term plan is to have PHP 7.0 become the minimum PHP version needed to run a WordPress site by December 2019.
So, if you update your PHP version of your website hosting to the latest one (for now it is PHP 7.x), then you will get rid of that “PHP Update Required” warning.