You can't do like this because when you create the first row then you have to decide how much will this column can span so you have to get the count of the similar ids first to achieve it. I am just giving you and idea how it can work with and array like you database provides.
<?php
// Array comming from database
$databaseValues = [
[
'item_id'=>'1001',
'item_color'=>'black',
],
[
'item_id'=>'1002',
'item_color'=>'blue',
],
[
'item_id'=>'1002',
'item_color'=>'green',
],
[
'item_id'=>'1003',
'item_color'=>'red',
]
];
// Creating an array as per the need for the table
$arrayForTable = [];
foreach ($databaseValues as $databaseValue) {
$temp = [];
$temp['item_color'] = $databaseValue['item_color'];
if(!isset($arrayForTable[$databaseValue['item_id']])){
$arrayForTable[$databaseValue['item_id']] = [];
}
$arrayForTable[$databaseValue['item_id']][] = $temp;
}
?>
<!doctype html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Document</title>
</head>
<body>
<table border="1">
<?php foreach ($arrayForTable as $id=>$values) :
foreach ($values as $key=>$value) :?>
<tr>
<?php if($key == 0) :?>
<td rowspan="<?= count($values)?>"><?= $id?></td>
<?php endif;?>
<td><?= $value['item_color']?></td>
</tr>
<?php endforeach;
endforeach; ?>
</table>
</body>
</html>
Hope this will be helpfull for you