5
you might be needing the leading slash on the REQUEST_URI environmental...
{if $smarty.server.REQUEST_URI == '/index.php'}
-or-
{if $smarty.server.REQUEST_URI|strstr:'index.php'}
-or-
{if $smarty.server.REQUEST_URI|strpos:'/index.php' === 0}
A cleaner approach would be to assign "page" variable to the smarty instance
$smarty->assign('page','index');
in which you can then test
{if $page == 'index'}
As any additional query string parameters on your index page will cause your very explicit match to fail
