PHP - Sort An Array But Ignore A Part Of The Values (better Explained In The Post)

if(isset($_POST['submit'])) {
/* Doesn't show if i put it after if($_POST['submit'] */
if(isset($_POST['grand_total'])) {
echo $_POST['grand_total'];
}

}

//A bunch of other html/php code. Another class calculates the subtotal assigns it the variable $subtotal



$cart_totals = new cartTotals($subtotal, $discounted_amount,$post_values->tip); // Cart class is shown below

/* Doesn't show if i put it before if($_POST['submit'] */
if(isset($_POST['grand_total'])) {
echo $_POST['grand_total'];
}
echo  "<input name='grand_total' type='hidden' value='$cart_totals->grand_total'  />"; // Shows the grand total after second from submission
echo "$cart_totals->grand_total"; // Shows grand total after the first submission

class cartTotals  {

	public $subtotal;
	public $sales_tax;
        public $tip;
	public $grand_total;
        public $discount_amount;
	public $href_page;
	public $invalidCouponMessage;
	const  TEST_ENVIORMENT = FALSE;


	/**
	 * [ Function gets constructed in the order summary where the [$discount_amount= ""]  arg does need to be passed.
     * But does get passed in when called on the checkout.php page. Therefore we set the default value to an empty string.]
	 * @param [float] $subtotal   [subtotal get passed in from the parent class coreCartFunction]
	 * @param string $discount_amount [The class checkCouponCode calculates this discount amount based on the
     * subtotal and the discount amount. It gets instantiated on the clients side and passed is this construction function.
     * This is all done on the checkout page.]
	 */

    /*The way the construct function works is by invoking all the methods the passed arguments
    When the methods get invoked the do all the work and set the properties its values. The properties then get echoed out
    on the client side.  */
	
    function __construct($subtotal="", $discount_amount= "", $tip=""){
    
    $this->subTotal($subtotal, $discount_amount);//SubTotal method takes the discount amount and subtracts it from the subtotal.
    $this->salesTax($subtotal, $discount_amount);
    $this->tip = $tip;
    $this->grandTotal();
	}

    private function subTotal($subtotal,$discount_amount) {

            $rounded_subtotal = round($subtotal-$discount_amount,2);
            $money_format_subtotal =  money_format('%i',$rounded_subtotal);
            $this->subtotal = $money_format_subtotal;
    }


    private function salesTax($subtotal, $discount_amount =""){
	$sales_tax = (STORE_SALES_TAX)?(float)STORE_SALES_TAX:8.875;
	$sales_tax =(($this->subtotal)*$sales_tax)/100;
	$sales_tax = round($sales_tax,2);
	$this->sales_tax = $sales_tax;
	}


	public function Tip() {
    //global $post_values;
    //$last_tip_selected = $post_values->tip > 0 ? $post_values->tip : "" ;
	$tip_output = "<select id='tip' name='tip'>";
 	for($tip=0.00; $tip<=11.75; $tip+=0.25){
 	if( $tip == "2") {$selected = " selected";} else {$selected ="";}
       $formatted_tip =  money_format('%i',$tip);

	$tip_output .= "<option {$selected} id='selected_tip' value='$formatted_tip'>"."$".$formatted_tip ."</option>".PHP_EOL;
		}

		$tip_output .= "</select>";
		return $tip_output;

    }

    private function grandTotal(){
        $grand_total = round($this->sales_tax+$this->subtotal+$this->tip,2);
        $grand_total_formatted =  money_format('%i',$grand_total);
        $this->grand_total = $grand_total_formatted;

    }

When i click my submit button i am posting the following.

		Array
(
    [submitStaffOrder] => 
    [staffMember] => Array
        (
            [0] => 2
            [1] => ANYCHEF1
        )

    [date] => Array
        (
            [0] => 2020-02-18
            [1] => 2020-02-18
        )

    [startTime] => Array
        (
            [0] => 11:01
            [1] => 10:10
        )

    [finishTime] => Array
        (
            [0] => 11:01
            [1] => 10:01
        )

    [delExisting] => Array
        (
            [0] => 
            [1] => toDel
        )

)

I would like to update/insert if delExisting is blank and delete if it has toDel in there.

I have the following but i am pretty sure the if is not working.

$date = $_POST['date'];
	$stime = $_POST['startTime'];
	$ftime = $_POST['finishTime'];
	$del = $_POST['delExisting'];
	$staff = $_POST['staffMember'];

$stmt = $conn -> prepare("
	                         INSERT IGNORE INTO ssm_staff_order (job_id, staff_id, staff_start_time, staff_finish_time, staff_start_date, staff_finish_date) 
	                         VALUES (?,?,?,?,?,?)
	                         ON DUPLICATE KEY 
	                         UPDATE 
	                         staff_start_time = VALUES(staff_start_time),
	                         staff_finish_time = VALUES(staff_finish_time);
	                         ");

	$delstmt = $conn -> prepare("
		                         DELETE FROM ssm_staff_order
		                         WHERE staff_id = ?
		                         AND job_id = ?
		                         AND staff_start_date = ?
		                         ");

	foreach ($staff as $key => $staffId) {
		if ($del == '') {
			$start = $date[$key].' '.$stime[$key];
			$finish = $date[$key].' '.$ftime[$key];
			$stmt -> bind_param('isssss', $jid, $staffId, $start, $finish, $date[$key], $date[$key]);
			$stmt -> execute();
		}
		

		
		if ($del == 'toDel') {
			$delstmt -> bind_param('sis', $staffId, $jid, $date[$key]);
			$delstmt -> execute();
		}
	}
	
}

Can i do what i am trying to do or am i way off here?

I struggle with arrays