HTML inside a PHP file is a common occurrence when building web applications, you can easily have a bootstrap page that uses PHP to show data.

You can either echo the html like:

$username = $data->username;
$date = $data->date;
echo "<h1>Welcome ".$username."</h1>";
echo "<h3>Today is the ".$date."</h3>";

or close PHP do some html open up PHP shortly closs it and do more html like:

$username = $data->username;
$date = $data->date;
?>
<h1>Welcome <?php echo $username; ?></h1>
<h3>Today is the <?php echo $date; ?></h3>

Now as to which is better? well performance wise they are the same, it just comes down to workflow, preferences and how clean it looks. For me i prefer the second one, especially when doing work in alot of colums and divs. The first one is good though for small, clean pages.