<a href='my_page.php?report_id=1'>Report 1</a>
<a href='my_page.php?report_id=2'>Report 2</a>

<?php

   if (isset($_GET['report_id']) {
     $report_id = $_GET['report_id'];
     if ($report_id =='1') {
         // ... generate the first report here
     }
     else if ($report_id=='2') {
         // ... do the other stuff here
     }
   }

?>