Questa la veloce prova che ho effettuato basandomi sull'esempio del manuale:

Codice PHP:
<?php
$xmlstr = '
<CBIBdySDDStsRpt 
    xmlns="urn:CBI:xsd:CBIBdySDDStsRpt.00.01.00" 
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
    xmlns:LMSG="urn:CBI:xsd:CBISDDStsRptLogMsg.00.01.00">

    <PhyMsgInf>...</PhyMsgInf>
    <CBIEnvelSDDStsRptLogMsg>
        <CBISDDStsRptLogMsg>
            <LMSG:GrpHdr>...</LMSG:GrpHdr>
            <LMSG:OrgnlGrpInfAndSts>...</LMSG:OrgnlGrpInfAndSts>
            <LMSG:OrgnlPmtInfAndSts>
                <LMSG:OrgnlPmtInfId>1</LMSG:OrgnlPmtInfId>
                <LMSG:TxInfAndSts>
                    <LMSG:OrgnlInstrId>11</LMSG:OrgnlInstrId>
                    <LMSG:OrgnlEndToEndId>00011</LMSG:OrgnlEndToEndId>
                    <LMSG:TxSts>RJCT</LMSG:TxSts>
                    <LMSG:StsRsnInf>...</LMSG:StsRsnInf>
                    <LMSG:OrgnlTxRef>
                        <LMSG:Amt>
                            <LMSG:InstdAmt Ccy="EUR">416.66</LMSG:InstdAmt>
                        </LMSG:Amt>
                        <LMSG:ReqdColltnDt>2015-07-10</LMSG:ReqdColltnDt>
                        <LMSG:CdtrSchmeId>
                            <LMSG:Nm>Sviluppo</LMSG:Nm>
                            <LMSG:Id>
                                <LMSG:PrvtId>
                                    <LMSG:Othr>
                                        <LMSG:Id>IT580010000006983211217</LMSG:Id>
                                    </LMSG:Othr>
                                </LMSG:PrvtId>
                            </LMSG:Id>
                        </LMSG:CdtrSchmeId>
                        <LMSG:PmtMtd>DD</LMSG:PmtMtd>
                        <LMSG:MndtRltdInf>
                            <LMSG:MndtId>BEQGT90000000000000162</LMSG:MndtId>
                            <LMSG:DtOfSgntr>2013-07-29</LMSG:DtOfSgntr>
                        </LMSG:MndtRltdInf>
                        <LMSG:RmtInf>
                            <LMSG:Ustrd>ADDEBITO 18 RATA</LMSG:Ustrd>
                        </LMSG:RmtInf>
                        <LMSG:Dbtr>
                            <LMSG:Nm>BOTTONE</LMSG:Nm>
                            <LMSG:Id>
                                <LMSG:PrvtId>
                                    <LMSG:Othr>
                                        <LMSG:Id>BTTGNN74H24F839N</LMSG:Id>
                                    </LMSG:Othr>
                                </LMSG:PrvtId>
                            </LMSG:Id>
                        </LMSG:Dbtr>
                        <LMSG:DbtrAcct>
                            <LMSG:Id>
                                <LMSG:IBAN>IT71D062300000035576740</LMSG:IBAN>
                            </LMSG:Id>
                        </LMSG:DbtrAcct>
                        <LMSG:DbtrAgt>
                            <LMSG:FinInstnId>
                                <LMSG:BIC>CRPPIT2P466</LMSG:BIC>
                            </LMSG:FinInstnId>
                        </LMSG:DbtrAgt>
                        <LMSG:Cdtr>
                            <LMSG:Nm>Sviluppo</LMSG:Nm>
                        </LMSG:Cdtr>
                        <LMSG:CdtrAcct>
                            <LMSG:Id>
                                <LMSG:IBAN></LMSG:IBAN>
                            </LMSG:Id>
                        </LMSG:CdtrAcct>
                    </LMSG:OrgnlTxRef>
                </LMSG:TxInfAndSts>
            </LMSG:OrgnlPmtInfAndSts>
        </CBISDDStsRptLogMsg>
    </CBIEnvelSDDStsRptLogMsg>
</CBIBdySDDStsRpt>
';

$xml = simplexml_load_string($xmlstr);
$xml->registerXPathNamespace('c', 'urn:CBI:xsd:CBISDDStsRptLogMsg.00.01.00');
$result = $xml->xpath('//c:MndtId');

foreach ($result as $MndtId) {
  echo $MndtId . "\n";
}
?>