- mb_substr: documentation ( source)
- strrpos: documentation ( source)
<?php
$domain['items']['dom'] = 'РФ';
$is_dot = strrpos($domain['items']['dom'], '.');
$domain_suffix = ($is_dot === FALSE )?$domain['items']['dom']:mb_substr($domain['items']['dom'],$is_dot+1);
echo $domain_suffix;