Design for mobile platform, what resolution to use?

Question

iPhone

Dear colleagues!
Faced the problem of choosing a resolution for mobile design. Design is not for the application! And for a regular phone browser, that is, this is an additional mobile version of the site.
What is the essence of the problem? I understand that at the moment there are many resolutions, but I don’t understand what size to draw at?! 480? 960? 1024? In fact, if you make rubber, then you can take the minimum size and not worry?!
Tell me how to approach this issue more professionally, how are you doing? The design will be uniquely touch and will not be designed for push-button phones.