I am designing an iPhone 6 app. I have set up my artboard to 750 X 1334px which I have found to be the standard size according to helpful websites. However, When convert the artboard size to inches it is 10.42 in x 18.53 in. Why is it so large? During exporting..is this when the actual asset size is found?
What determines the physical dimensions of your image (i.e. Inches) is the resolution (PPI). If you set your Photoshop document to the same pixel dimension and PPI as an actual iPhone screen (which Google reports is 326 PPI) then it will report the same physical dimensions.
But, you don't need to. The only time you need to worry about physical dimensions is when you print your document. Resolution (as in PPI) is only meta data, it doesn't actually affect your image. If you are designing for screens then you can forget about the resolution. 72 PPI is the de-facto standard so you can use that, but it doesn't really make a difference.
Unless you actually do want to print your designs at actual size, then yes—set your PPI to the same as an iPhone 6.