Rapidweaver iphone pictures

I am using Tesla Pro to build a website and all is good until i preview it on iphone. Most of the traffic towards my website will be 60% mobile and the rest is split between ipads and desktop.
What size do the banners need to be so when viewed on iphone they don’t get cut off to silly portions of the actual banner jpg

i have photobulk to resize my banners or could i delete the entire banners altogether and use DropOnImage Stack to manage my banner images?

PLEASE advice