Is it legal to sell an iPhone without a charging box?

Yes, of course it's perfectly legal. In fact, in the EU it became required by law to stop including chargers with electronic devices. Most people have them already. And if by chance they don't, then they can buy one. I can assure you, I have more than enough chargers.

Due to environmental concerns, a charger is not included with every purchase. It has been that way for 4 years now and Apple has transitioned to USB-C so the cable will work with all standard chargers. This reduces e-waste by the chargers not ending up being in the landfills and the same is true for other device manufacturers such as Samsung where they are no longer included. Most phone purchases are from users replacing a phone and they can continue to use their previous charger. Other users may use a wireless charging puck and have no need for the charger. If you are not using wireless charging now, I would recommend it for the convenience alone.

You can feel however you want, but what Apple is doing is perfectly legal.

Why wouldn’t it be legal? After all it is legal to sell gasoline in a can at a gas station without the obligation of including a car in order for you to use the gasoline.

Right?

Other opinions are available. I've got a large drawer full of USB power supplies and I certainly don't want any more. If you really need another PSU when you buy and iPhone then ........ buy one. As for the cable - I've got a box full of them, most of them still coiled up with the Apple cardboard.