This is possible if you want.
Do the following in ./include/staff/tickets.inc.php:
Change
$sortOptions=array('date'=>'ticket.created','ID'=>'ticketID','pri'=>'priority_urgency','dept'=>'dept_name');
into
$sortOptions=array('date'=>'ticket.created','ID'=>'ticketID','pri'=>'priority_urgency','dept'=>'dept_name','pho'=>'phone');
Change
$qselect = 'SELECT ticket.ticket_id,lock_id,ticketID,ticket.dept_id,ticket.staff_id,subject,name,email,dept_name '.
',status,source,isoverdue,ticket.created,pri.*';
$qfrom=' FROM '.TICKET_TABLE.' ticket LEFT JOIN '.DEPT_TABLE.' dept ON ticket.dept_id=dept.dept_id '.
' LEFT JOIN '.TICKET_PRIORITY_TABLE.' pri ON ticket.priority_id=pri.priority_id '.
' LEFT JOIN '.TICKET_LOCK_TABLE.' tlock ON ticket.ticket_id=tlock.ticket_id AND tlock.expire>NOW() ';
into
$qselect = 'SELECT ticket.ticket_id,lock_id,ticketID,ticket.dept_id,ticket.staff_id,subject,name,email,dept_name '.
',status,source,isoverdue,ticket.created,ticket.phone,pri.*';
$qfrom=' FROM '.TICKET_TABLE.' ticket LEFT JOIN '.DEPT_TABLE.' dept ON ticket.dept_id=dept.dept_id '.
' LEFT JOIN '.TICKET_PRIORITY_TABLE.' pri ON ticket.priority_id=pri.priority_id '.
' LEFT JOIN '.TICKET_LOCK_TABLE.' tlock ON ticket.ticket_id=tlock.ticket_id AND tlock.expire>NOW() ';
Change
<th width="70">
<a href="tickets.php?sort=pri&order=<?=$negorder?><?=$qstr?>" title="Sort By Priority <?=$negorder?>">Priority</a></th>
into
<th width="70">
<a href="tickets.php?sort=pho&order=<?=$negorder?><?=$qstr?>" title="Sort By Phone <?=$negorder?>">Phone</a></th>
and change
<td class="nohover" align="center" style="background-color:<?=$row?>;"><?=$row?></td>
into
<td class="nohover" align="center"><?=$row?></td>
Off course it's also possible to add another row if you want. Try to adjust the code as you see fit.