<?php
$xml = <<<EOT
<?xml version="1.0" encoding="utf-8"?>
<soap:Envelope xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/">
  <soap:Body>
    <InformacijaOPosiljci xmlns="http://TrackTrace.com">
      <strPrijemniBroj>CH176197243US</strPrijemniBroj>
    </InformacijaOPosiljci>
  </soap:Body>
</soap:Envelope>
EOT;

$headers = [
    "Content-Type: text/xml; charset=utf-8",
    "Cache-Control: no-cache",
    "Pragma: no-cache",
    "Content-Length: ".strlen($xml)
];

$curlh = curl_init();

curl_setopt($curlh, CURLOPT_URL, 'https://e-racuni.postacg.me/TTService/Service1.asmx');
curl_setopt($curlh, CURLOPT_RETURNTRANSFER, true);
curl_setopt($curlh, CURLOPT_TIMEOUT, 10);
curl_setopt($curlh, CURLOPT_POST, true);
curl_setopt($curlh, CURLOPT_POSTFIELDS, $xml);
curl_setopt($curlh, CURLOPT_HTTPHEADER, $headers);

$resp = curl_exec($curlh);

curl_close($curlh);

$xml = new SimpleXMLElement($resp);

$xml->registerXPathNamespace('d', 'urn:schemas-microsoft-com:xml-diffgram-v1');

$tables = $xml->xpath('//TableName');
foreach ($tables as $table) {
    echo $table->Opis . PHP_EOL;
}