How much tax do you pay for iPhones?

That would depend on what state you purchase it in if you're in the US. or what your government charges in different parts of the world.

Here are each state's tax rates in the US. -

https://taxfoundation.org/data/all/state/2023-sales-tax-rates-midyear/

It depends on the tax rate where you buy. Might be in the range of 5-7% more or less in the U.S. Taxes tend to be higher in Europe.