PHP foreach code performance speed

$venueIDS = isset($_POST['location']) ? $_POST['location'] : array();

$msg = $_POST['message'];

$text = "";
$destination = "";
$content = "";
$response_lines = array();
$smsbroadcast_response  = "";
$message_data = array();

if(!empty($venueIDS)){

        $Members = GoldCardMembers::MembersMobileByVenue();
        foreach($Members as $Member){ // O(n) size of $Members
            if(in_array($Member->Venue, $venueIDS)){ // O(v) size of $venueIDs

                $destination = rawurlencode($Member->Phone);
                $text = rawurlencode($Member->FirstName . ' ' .$msg);

                $content =  '&to='. $destination .
                            '&message=Hi ' . $text . '. Reply STOP to opt out'.
                            '&ref=Members';

                $smsbroadcast_response = sendSMS($content);
                $response_lines = explode("\n", $smsbroadcast_response); // O(r) number of "\n" occurances

                 foreach( $response_lines as $data_line){ // O(r)

                    $message_data = explode(':',$data_line); // O(d) number of ":" occurances

                    if($message_data[0] == "OK"){
                        echo "The message to ".$message_data[1]." was successful, with reference ".$message_data[2]."\n";
                    }elseif( $message_data[0] == "BAD" ){
                        echo "The message to ".$message_data[1]." was NOT successful. Reason: ".$message_data[2]."\n";
                    }elseif( $message_data[0] == "ERROR" ){
                        echo "There was an error with this request. Reason: ".$message_data[1]."\n";
                    }
                 }
            }
        }
}

Here's a list of what I did:

• removed the for loop from bottom and echo the $message directly from the main loop instead
• removed $ref var
• initialized $destination, $text, $content, $response_lines, $smsbroadcast_response and $message_data vars outside the for loop since declaring them inside the loop with each iteration is sub-optimal

That's all I can think about for now.

Notes for further improvements:

I'd investigate on the performance of sendSMS that you're using. It could be one of the components that are slowing things down.

In order to dig deeper, a helpful tool for analyzing performance is big Oh notation. So I've added comments to label loop components.

Because we're looking at multiple nested loops we generally have something like O(N^3) here.

However, we could write that equation to be more detailed such as this:

O( n * (v + 2r) * d)

(please check code comments to see what each variable represents)

Since you're asking for a high "n" (number of members) I'd investigate ways to make the other variables like "v", "r" or "d" smaller.

Eliminating any of these variables altogether like removing

$message_data = explode(':',$data_line);

have the highest positive impact on performance (given that is still achieves the same functionality).