Why Does My Online Store Struggle On Mobile Phones?

A few months ago, my cousin noticed that people visited her online store but hardly placed any orders. She checked the prices and products, but everything seemed fine. Later, we opened the website on a phone and found the real problem. The text was too small, pictures looked messy, and the order button was hard to find. We made the layout simpler, fixed the images, and made the buttons easier to use. Learning about mobile responsive web design UK helped us understand the issue better. Have you faced something similar, and what worked for you?