Why is your iPhone twice as expensive as in the apple store?

Hi all,

I'm trying to figure out the prices for a mobile plan with an iPhone 5s:

Unlimited calls and text and 2 GB of data plan goes for 55$.

If I now chose an iPhone:

For a phone I pay 40$ a month and an upfront of 235$. I am locked to the contract for 24 months.

235$ upfront and 24 payments of 40$. That equals a total cost of the phone of

1195$

or almost twice of what I would have to pay if I bought the phone in an apple store. What do I miss?

Thanks!