Check for a specific PHP version from a WordPress plugin

plugin.php

//Load the current WP core version
include( ABSPATH . WPINC . '/version.php' );
if (version_compare($wp_version, '5.3') < 0) {
    //If WP core is < 5.3, do a PHP version check ourselves
    $php_version = phpversion();

    if (version_compare($php_version, '7.1') < 0) {
        die('This plugin requires PHP 7.1 or higher');
    }   
}