An alternative that might make sense especially if this test is being made multiple times and you are running PHP 7+ and have installed the Set
class is:
use Ds\Set;
$strings = new Set(['uk', 'in']);
if (!$strings->contains($some_variable)) {
Or on any version of PHP you can use an associative array to simulate a set:
$strings = ['uk' => 1, 'in' => 1];
if (!isset($strings[$some_variable])) {
There is additional overhead in creating the set but each test then becomes an O(1) operation. Of course the savings becomes greater the longer the list of strings being compared is.