How does my iPhone know I'm in the US if iI changed the appstore and date/time to UK?

I'm DYING to use the ITV app to watch my favorite UK T.V. Shows, thought I live in the US.

I have successfully switched from the US to UK app store and was able to download the ITV app. Since I'm using an old iPhone of mine, it is on airplane mode and I'm using Wi-Fi since I do not have cellular connection (didn't want to use my actual iPhone incase something in the process messed it up). When I open the app it tells me to enter a postal code and I enter one from the UK. However, when I try to watch a video, it says that i can "only view the content if I'm in the UK

If I'm in airplane mode and I'm using a UK appstore/date and time, how does it know that I'm in the US? How do i change that/are there any other settings i need to chage?

Well if you are connected to Wi-Fi, the IP is indicative of your true location,
if connected to 4g/3g etc. The cellphone tower is indicative of location
and if your GPS is on, that is indicative of your true location

So far as the phone network goes your phone knows where it is because it'll be connected to the US cellular phone network, but that's not actually the information you need. What you're referring to is when using the internet. Regardless of whether you connect to the internet via the cell network or your home router your phone will be assigned an IP address which is not one of those used in the UK, so ITV's server will know you're abroad and will block you. The only way to get around that is to connect to it via a proxy server based in the UK.