使用ob_start（）从外部文件获取邮件模板

I have two files:

function emailTemplate() {
        if($this->template) {
            extract($this->email_data);
            ob_start();
                include_once("email_templates/".$this->template.".phtml");
            return ob_get_clean();
        }
}

and email template .phtml

<div>Hello, Your order has been accepted. <?= $some_data ?></div>

PHPmailer code:

$mail = new PHPMailer();
        $mail->SetLanguage("cz");
        $mail->IsSMTP(); 
        $mail->Host = "smtp.some.cz";
        $mail->SMTPAuth = true; 
        $mail->Username = "info@some.cz";
        $mail->Password = "xysdff";
        $mail->From = "info@some.cz";
        $mail->FromName = "Some.cz";    
        $mail->AddAddress($this->xy);
        $mail->AddBCC($this->xy2, 'potvrzení');

        $mail->IsHTML(true);
        $mail->Subject = $subject;

        $mail->Body = $template;

        $mail->AltBody = $template;
        $mail->WordWrap = 50;
        $mail->CharSet = "utf-8";
        }

        if(!$mail->Send()) {
            throw new Exception($mail->ErrorInfo);
        }

I send this email via PHPmailer, but it keep telling me that body of an email is empty but i get the email with right formating and data. Just this error message keep showing up. if i change include_once for just include, it send me two emails instead of one.

I don't see where the problem is

Thanks for help

EDIT: email came with normal data a right formated and second came empty...