Understanding how a phone bill works?

So for Christmas, I plan to accumulate money and buy the latest iPhone or at least one of the latest models. My family is currently using Verizon and running all non apple phones. I'm curious to what a phone bill actually pays for. Like, if I were to pay the phone in full, would I have to pay monthly? And I've heard that apple bills are more expensive? Is that just because the phone costs more and that is the price broken up between months? Also does the phone bill change depending on how many phones are on the plan?

If you buy an UNLOCKED phone outright you can pick any airtime provider.
Apple phones tend to eat data. Get a good data plan.
If you buy a phone from a provider the bill is made up of 2 parts.
Airtime and payments on a loan to buy the phone.
As Apple phones are very expensive this is more than most Android phones.
Owned outright you can chose a pay monthly sim or a PAYG Sim.
These tend to have poor data allowences.
I have a Sim only deal as I own my phone.
No tie in loads of data and minutes at a low rate.

It's complicated - because there are so many different ways.

1) You could pay the phone in full (somewhere around 800$ for the 8, around 1000$ for the X IIRC), then get any prepaid, PAYG or contract SIM for the phone. In the case of the contract SIM, you will pay a monthly fee plus whatever you use in terms of services that are not included in that fee, in the other case, you will pay for all services that you use (since usually none are included). However, what you pay for what kind of service (landline calls, mobile calls, data) will differ between these options and different rates within the options.

2) You could pay just a nominal fee for the phone from a provider and get a specific SIM for the phone. In this case, you're usually locked to the provider you bought the phone from for the duration of the contract, and you'll pay back the phone over the duration of the contract (and then some). This means that _usually_, for the same services, in this case you'll pay more per month than in the first option.

3) You could find a reseller who will sell you the phone at full market price (maybe a bit above) and then credit you with (a part of) their bonus for selling you a contract. This is what I usuall do - find a top phone that is maybe two years old and discounted, then get a contract extension for my existing contract. This lets me get an unlocked phone for free to little money, while not paying more for the contract I would use anyways. No idea who these resellers would be in the US, though - I'm in Germany.