This is the code I found for phone in viewticket.inc.php:
<tr>
<th>Phone:</th>
<td><?=Format:($ticket->getPhoneNumber())?></td>
</tr>
<tr>
Commented out:
<tr>
<th>Phone:</th>
<td><?=Format:($ticketgetPhoneNumber())?></td>
</tr>
<tr>-->
The one thing to be mindful of is that if you do intend to use it in future and re-display that field all data will be blank and it might take some time to re-populate it all. Hope this helps.
Rich