Making photographic prints same width on mobile product list page

I have 4 different types of photographic prints for sale: square, landscape and two different ratios of portrait. 

Can anyone help with code to make these all have the same width only on a mobile phone?

(As a general point for products I've set ratio to 3:2 standard, then tagged all portrait shots as 'portrait' - not sure if that makes a difference to my question) 

Cheers

Hi. Can you share link to your site? We can check easier