How to take normal text from database table and change according to defined variable from other database table

public function customer_bill_reminder()
{
    if($this->session->userdata('role') == "ADMIN" || $this->session->userdata('role') == "SUPER ADMIN")
    {

        $from = $this->input->post('from');
        $to   = $this->input->post('to');
    
        $result = $this->MAILModel->customer_sms_reminder($from,$to);
        $result2 = $this->MAILModel->auto_sms_reminder();

        foreach($result2 as $row)
        {
            $message = @$row->sms_template;
        }

        foreach($result as $row)
        {
            $phone_number = @$row->mobile;
            $year = @$row->bill_period;
            $control_number = @$row->control_number;
            $amount = @$row->bill_amount;
            $message = "You will pay $amount in $year";
           
            echo $message;

            $this->NotificationModel->send_sms($phone_number,$message);
        }
    }
}

The above hard coded text from $message will change $amount and $year. I have problem since the text is from the database - when I echo nothing happens, it will output exactly as it is.

I want to get the output as exactly the hard-coded text but it should be from the table.

     $message1    = str_replace('$amount',$amount,$message);

     $message2=str_replace('$phone_number',$phone_number,$message1);
     $message3=str_replace('$control_number',$control_number,$message2);
     $message4=str_replace('$year',$year,$message3);
     $this->NotificationModel->send_sms($phone_number,$message4);