public function lookupKey($key)
{
if (count($this->phonePrefixMapStorage) == 0) {
return null;
}
while (strlen($key) > 0) {
if (array_key_exists($key, $this->phonePrefixMapStorage)) {
return $this->phonePrefixMapStorage[$key];
}
$key = substr($key, 0, -1);
}
return null;
}