This script will gives your the required output
<?php
$payload = 'job.xml';
$results = simplexml_load_file($payload);
foreach($results->OBX as $obx)
{
//var_dump($results);
$test = $obx->{'OBX.5'}->{'OBX.5.1'};
$testresult = $obx->{'OBX.3'}->{'OBX.3.2'};
echo $testresult .' : '.$test.'<br/>';
}