How to get the NodeValue from <td> type input

I am using this HTML and I am trying to parse it to get the nodeValue of all the elements in the table columns.

<table id="custinfo">
    <tr>
        <td><label>First Name</label></td> 
        <td><input type="text" name="firstname" ></td>    
    </tr> 
    <tr>
        <td><label>Last Name</label></td>
        <td><input type="text" name="lastname" ></td>   
    </tr>
    <tr>
        <td><label>Phone Number</label></td> 
        <td><input type="text" name="email" ></td>
    </tr>   
</table>

Here is the PHP It's only working for the labels but not for the input types.

$Dom= new DOMDocument();   
libxml_use_internal_errors(true);
$Dom->loadHTMLFile('Pre_order.html'); 
$info=$dom->getElementById('custinfo');
$inforows=$info->getElementsByTagName("tr");
$input_tags = $dom->getElementsByTagName('input'); 
$fnamecol=$inforows->item(0)->getElementsByTagName("td");
$fname=$fnamecol->item(1)->nodeValue; //this is returning null Instead of returning the input text value.

Use simple_dom_parser.php library instead (Download library: https://sourceforge.net/projects/simplehtmldom/files/ & docs: http://simplehtmldom.sourceforge.net/)

require_once('simple_dom_parser.php');

// Create DOM from file
$html = file_get_html('Pre_order.html');


// Find all labels
foreach($html->find('label') as $label)
       echo $label->plaintext . '<br>';


// Find all inputs
foreach($html->find('input') as $input)
       echo $input->name . '<br>';