AT&T help, am I able to upgrade without raising monthly rates?

I currently have an iPhone 5c. Yes I know old lol and I'm wanting to purchase an iPhone 8 from AT&T full price for $699. We don't have the AT&T Next thing. Would our rates go up just for one phone?

We have NO idea what your contract with AT&T says.

You must talk with them to find out what your options are and if there will be any charges.

You can have any phone you can pay cash for, and that is the way to buy phones.

If you buy it upfront there will be no change to your service rates (aside from a one time activation fee). The raise of monthly rates are the cost of the device cut into installment billing like a car payment.