I thought it will be good practice to set the variables in advance, even if they are empty values.
For the last part, I see your point of the header & footer but this 2 parts contains the main html block of creating a page and also the incuded files needed to make it work.
The reason I used it to create them separate is because in the case of jquery mobile pages, the could be more than one page id accessed by hash key using ajax and cant have 2 doctype in my code, if you know what I mean.
<?php include("_funct_header.php");
$page1 = new create_page();
//add doctype & includes
echo $page1->add_header_mob();
//add content to the page
$page1->title = '<h1>Home</h1>';
echo $page1->new_page("page1",$page1->title, "content - can be dynamic or static :)", "footer");
/* PAGE 2 */
$page2 = new create_page();
//PAGE HEADER & BACK BUTTON
$page2->title = $page2->add_back_btn().'<h1>Header 2</h1>';
//page 2 content
echo $page2->new_page("page2", $page2->title, "Content 2", "Footer 2");
//add closing HTML footer
echo $page1->add_footer();
?>