all for processing MUST happen on the forms action page.
this code on the search page:
<?php
if (!session_id()) session_start();
if (isset($_POST["searchSubmit"])) {
$_SESSION["searchFieldValueMobi"] = "".((isset($_POST["searchField"]))?$_POST["searchField"]:"") ."";
}?>
will not do anything since the form posts to the results page.
you need to out that code on the results page.