PHP MYSQL need to group rows that have same value in certain column

I suggest you fetch all the entries and group them with php like so;

global $wpdb;
$rows = $wpdb->get_results( "SELECT * FROM entries");
$originators = [];
foreach($rows as $row)
{ 
    $originators[$row->originator][] = $row;
}

then loop through the originators to fill the table, something like this:

<?php
foreach($originators as $originator => $entries){
?>
   <table class="table">
    <thead>
      <tr>
        <th>Originator</th>
        <th>Collaborator</th>
        <th>engagement_partner</th>
        <th>Niche</th>
        <th>Fee Potential</th>
    </tr>
    </thead>
    <tbody>
    <?php foreach($entries as $entry){ ?>
        <tr>
            <td><b> <?php echo $entry->originator; ?></b></td>
            <td><?php echo $entry->collaborator; ?></td>
            <td><?php echo $entry->engagement_partner; ?></td>
            <td><?php echo $entry->niche; ?></td>
            <td><?php echo $entry->fee_potential;?></td>
        </tr>
    <?php } ?>
    </tbody>
</table>
<?php}?>

It doesn't looks like a GROUP BY statement is what you are looking for.

Seeing your example HTML structure, the thing you are looking for is an ordered list of rows. You can then use php to sort the results and then use them

global $wpdb;
$rows = $wpdb->get_results( "SELECT * FROM `entries`");
$sortedRows = [];
foreach($rows as $row) {
    if (!isset($sortedRows[$row->originator])) {
        $sortedRows[$row->originator] = [];
    }
    $sortedRows[$row->originator][] = $row;
}

a different approach is using ORDER BY in the query, which i won't fully work out since i dont know what your approach is on creating the HTML structure:

global $wpdb;
$rows = $wpdb->get_results( "SELECT * FROM `entries` ORDER BY `originator` ASC");
$currentOriginator = NULL;
foreach ($rows as $row) {
   if ($row->originator !== $currentOriginator) {
       //create table
       $currentOriginator = $row->originator;
   }
   //add the row to the table
}