Testimonial grid section using CSS grid and Flexbox

I used flexbox to make the layout responsive from the mobile width to the desktop width, and at the desktop width I switched to grid for the final layout. What I was going for was more of a masonry look in-between the mobile and desktop layout but I couldn't get it to work just using grid or flexbox. I'd love to hear any suggestions on how I might have done that as well as any other feedback. Thank you!