Repositories

CustomerRepository.php

<?php

interface CustomerRepository
{
    public function isPremiumCustomer(CustomerId $customerId) : bool;

    // ... more API (fetch collections, filter, etc):
    public function findAllPremiumCustomer() : PremiumCustomersList;
    public function findAllPremiumCustomerIds() : PremiumCustomersIdList;
}

Order.php

<?php

// this is your aggregate
class Order
{
    // ... 
    public static function placeForPremiumCustomer(
        CustomerRepository $existingCustomers,
        CustomerId $customerId,
        $foo,
        $bar
    ) : self {
        if (! $existingCustomers->isPremiumCustomer($customerId)) {
            throw CustomerIsNotAPreviousCustomer::fromCustomerId($customerId);
        }
        
        return new self($customerId, $foo, $bar);
    }
    
    // ...
}

PlaceOrderForPremiumCustomerCommandHandler.php

<?php

class PlaceOrderForPremiumCustomerCommandHandler
{
    private $customers;
    private $oders;

    public function __construct(CustomerRepository $customers, OrderRepository $orders)
    {
        $this->customers = $customers;
        $this->orders    = $orders;
    }
 
    public function handle(PlaceOrderForPremiumCustomerCommand $command)
    {
        $this->orders->store(Order::placeForPremiumCustomer(
            $this->customers,
            $command->customerId,
            $command->foo,
            $command->bar
        ));
    }
}