用形式动作后置方法代替获取按钮的值

Problem Statement: Get value of button in PHP, without form-action-post method.

Overview: Developing a web application to manage time-sheet of employees,

  1. User selects current project, and fills his/her time according to task assigned.
  2. After s/he fill, submits time-sheet to his/her manager. enter image description here

Code(to display pre-defined projects from DB, enter_time.php)

<!DOCTYPE html>
<html>
<head>
...
</head>
<body>
<form action="enter_time.php"  method="post">
<?php if (is_array($separateProjects) || is_object($separateProjects)):?>
<?php foreach ($separateProjects as $val):?>

<?php if(strcmp($_SESSION['project_selected'],$val)==0):?> 
<button style="float:left" class="btn-default active-project" name="PROJECT" type="hidden" value="<?php echo $val ?>">  
<?php echo $val ?></button> 
<?php else: ?> 
<button style="float:left" class="btn-default inactive-project"  name="PROJECT" type="hidden" value="<?php echo $val ?>">  
<?php echo $val ?></button>
<?php endif; ?>
<?php endforeach; ?>
<?php endif; ?>
</form>
  ...
</body>
....
</html>

Code( when user selects particular project, enter_time.php):

function projectDisplay()
  {
      $_SESSION['project_selected'] =$_POST["PROJECT"];
  };

  if(isset($_POST['PROJECT']))
  {
     projectDisplay();
  }

Question: How do i get value of button in PHP, without form-action-post method? and save that value on _SESSION variable?.

Reason: When user selects particular project from list (clicks on project name button), entire page gets refreshed, and all other values of the screen example date,task list, etc get reset, and i am storing this project value in _SESSION variable for the further processes.

I am happy to any missing detail(s) if any. Help would be appreciated.