PHP uses reference counting to manage base types.

<?php
// refcount = 1
$name = "Sterling";
// refcount = 2 (no copy)
$newname = $name;
// refcount = 2
echo $name;
// $newname is copy of $name, $newname refcount 1
// $name refcount 1
$newname .= " Hughes";
// refcount = 1
echo $newname;
?>
To avoid copy-on-write, you would use the alias operator (&).

<?php
// refcount = 1
$name = "Sterling";
// refcount = 2, is_ref
$newname = &$name;
// refcount = 2
$newname .= " Hughes";

// Sterling Hughes
echo $newname; 
// Sterling Hughes
echo $name;
?>