<?php

namespace Customize\Form\Extension\Admin;

class OrderTypeExtension extends AbstractTypeExtension
{
    /**
     * {@inheritdoc}
     */
    public function buildForm(FormBuilderInterface $builder, array $options)
    {
        $Order = ???;    // ★ どうやって取得する？
        $Sender = $this->senderRepository->findOneBy(['Customer' => $Order->getCustomer()]);

        $builder
            ->add('Sender', SenderType::class, [
                'data' => $Sender,
            ])
        ;
    }

    /**
     * {@inheritdoc}
     */
    public function getExtendedType()
    {
        return OrderType::class;
    }
}

$Order = $options['data'];