最后一行代码

return $nodes->item(0)->nodeValue;

因为只返回item(0)
所以只看得到一个100
只需检测$nodes的长度，循环输出即可
代码

<?php
$xmlstring = '<?xml version="1.0"?>
<!DOCTYPE GetUserInfo>
<GetUserInfo>
<Customer>id*cn</Customer>
<GeocallCLI>100</GeocallCLI>
<GeocallCLI>101</GeocallCLI>
<GeocallCLI>102</GeocallCLI>
<GeocallCLI>103</GeocallCLI>
<GeocallCLI>105</GeocallCLI>
</GetUserInfo>';

$xmldoc = new DOMDocument();
$xmldoc->loadXML($xmlstring);
$users = $xmldoc->getElementsByTagName('GetUserInfo');
$html  = '';
foreach ($users as $user) {
    $html .= get_txt($user, 'Customer') . '
';
    $html .= get_txt($user, 'GeocallCLI') . '
';
}
echo $html;

function get_txt($parent, $name)
{
    $nodes = $parent->getElementsByTagName($name);
    
    $data = '';
    for ($i = 0; $i < $nodes->length; $i++) {
        $data .= 'output' . $name . ':' . $nodes->item($i)->nodeValue . '<br/>';
    }
    return $data;
}
?>

可否代码示例,谢谢!