UpFront web page not showing all elements on small screens

Hi, I've been working on the ladiesthatplan.com website using the UpFront theme. I've not used it before but am slowly getting to grips with it, however, when I shrink my screen up on my imac or if I open the website on my iphone, it is missing chunks of content.

If you see the homepage, only 1 of the 4 bottom sections show on the iphone and yet they all show on the computer.

I sell a lot of products via smart phones so it's really important the website works on those devices.

Can you tell me what is going wrong and how I can fix it please?

Thank you
Sophie