The same thing happened with iPods back in the day. The first couple generations came in these fat cubic boxes with cables, headphones, an installation CD, a printed manual, and a charging brick. The 3rd gen was probably peak packaging as it also game with plastic adapter inserts for licensed 30-pin adapter products and both FireWire and USB cables. The 5th gen iPod came in a much flatter box, probably a third the height of the old ones. That meant an freight container or UPS truck could carry three times more iPods. The iPod mini vs nano was very similar in terms of packaging savings.
Besides the better shipping efficiency it's also worth considering the real estate. Retailers, including Apple's own stores, have finite storage space for products. The new iPhones come in multiple colors for each model. Shrinking the packaging dimensions means a wider selection can be kept in stock in the same space as a narrower selection of the previous model.
Regardless, at the scale of Apple selling iPhones a small decrease in weight and/or better packing efficiency can mean huge CO2 savings. A gallon of diesel producers about 20 pounds of CO2. Doubling the iPhone/mile because of smaller packages halves the CO2/iPhone production.
Besides the better shipping efficiency it's also worth considering the real estate. Retailers, including Apple's own stores, have finite storage space for products. The new iPhones come in multiple colors for each model. Shrinking the packaging dimensions means a wider selection can be kept in stock in the same space as a narrower selection of the previous model.
Regardless, at the scale of Apple selling iPhones a small decrease in weight and/or better packing efficiency can mean huge CO2 savings. A gallon of diesel producers about 20 pounds of CO2. Doubling the iPhone/mile because of smaller packages halves the CO2/iPhone production.