The second parameter spicifies if the object is write in multipage file (true) or split every page in a single file (false).
Example:
<?php
$multiTIFF = new Imagick();
$files = scandir($mytifspath);
foreach( $files as $f )
{
$auxIMG = new Imagick();
$auxIMG->readImage($mytifspath.$f);
$multiTIFF->addImage($auxIMG);
}
//file multi.TIF
$multiTIFF->writeImages('multi.TIF', true);
//files multi-0.TIF, multi-1.TIF, ...
$multiTIFF->writeImages('multi.TIF', false);
?>