How to Get order increment id using order id in Magento 2

You have to pass \Magento\Sales\Api\OrderRepositoryInterface in construct of your class.

protected $orderRepository;

public function __construct(
    ..., 
    \Magento\Sales\Api\OrderRepositoryInterface $orderRepository
){
    ...
    $this->orderRepository = $orderRepository;
}

Then you can do following:

$order = $this->orderRepository->get($orderId);
$orderIncrementId = $order->getIncrementId();