Interesting. I generally just use the original iPhone boxes. I know most recyclers don't need you to send them - but I have no need for it beyond selling the phone... And I always hold onto the box incase I make a private sale or any particular recycler gives a higher valuation if you include the box (a couple do).I can see why many on here used the box from the ESR Amorite protectors, to send your phones off to MM - its the perfect size and strength to house an iPhone !!
I also know that with photos of the phone before being sent, and sending in the official Apple box designed to withstand shipping - we receive them often in bags without bubble wrap in the first place - no-one can argue that damage has been caused by the packaging used... Not the recycler, and not Royal Mail in the case of a claim...