Best plugins to make website look good mobile?

I’m working on an insurance and real estate website, and using the Tesseract theme. It claims to be a responsive theme, but when I view my site on my phone, the background images of my rows are cut off. I want to see the entire image across my phone screen and not just the left side of it.

Anybody recommend a good mobile plugin? (can be free or cost money) I like the look of my site on a desktop but mobile is lacking.

Link: https://staging.tasullivanagency.com/

Thanks!