can't use include file with php tags

While attempting to assign the array elements of an include file to a
variable the php tags embedded in the include file fail to
interpolate. What am I missing?

$t_file = file($PATH_DOCS . '/inc/navElem.inc.php');
$iw_mast .= $t_file[0];

undesired output:
<ul><li><a href="<?php echo $absPath; ?>/<?php echo $p0_file;
?>.php"><?php echo $p0_label; ?></a></li></ul>

would like to get:
<ul><li><a href="localhost/filename.php">link text</a></li></ul>

Thank you.
.