strtotime() is fine, but it runs the risk of returning unexpected results due to the date configuration of your system. Just to be extra safe, I favour using a look-up array.
<?php
function dateReformat( $date )
{
$monthList = array
(
'January',
'February',
'March',
'April',
'May',
'June',
'July',
'August',
'September',
'October',
'November',
'December'
);
$tmp = explode( '/', $date );
$month = $monthList[ $tmp[1]-1 ];
return "{$tmp[0]} {$month} {$tmp[2]}";
}
echo dateReformat( '12/05/1980' );