Just try like this:
HTML in PHP :
$link_address1 = 'index.php';
echo "<a href='".$link_address1."'>Index Page</a>";
$link_address2 = 'page2.php';
echo "<a href='".$link_address2."'>Page 2</a>";
Easiest way
$link_address1 = 'index.php';
echo "<a href='$link_address1'>Index Page</a>";
$link_address2 = 'page2.php';
echo "<a href='$link_address2'>Page 2</a>";