Before 2007, when there were no iPhones, there were no responsive websites. They were all displayed on a relatively large screen. But when the iPhone came along, new demands were placed on websites
Today, it is unthinkable to launch a new website without it being responsive. Responsive means that the website adapts to the size of the screen, but also how the screen is facing (horizontally or vertically).
Today, there are several screen sizes:
What's more, users are so inventive that they turn their smartphones and tablets both horizontally and vertically.
This placed completely new demands on web developers. Some solved this by creating a mobile version, typically called m.domaene.dk. When a user came from a mobile, he was sent to this domain. Many failed by not sending people the other way. A typical scenario was that the user shared a link from their mobile to a user sitting on a desktop. When they opened the mobile version, they got a miserable experience. So now it was suddenly the desktop users who sometimes got a lousy experience instead of the mobile users.
Soon after, the concept of a responsive website was introduced. This means that the site adapts to the size of the screen and is created with something called "media queries". Here you specify how things should behave on different screen resolutions. Sometimes you remove elements on mobile and sometimes you make things bigger.
Yes... in 2019, your online store must be responsive. This applies to all websites. There is no way around it. Both for the sake of users, but also for the sake of your SEO efforts. Google penalizes sites that are not mobile-friendly. So it's an ultimate requirement when developing new sites.
In addition to physically testing it on your own smartphone, you can also test your website on this page from Google.
Another good idea is to go to Power or Elgiganten and test your website on the many mobiles and tablets they have on display.
We've been working with online marketing ourselves for decades. As the only shop system in the country, we have spoken multiple times at conferences such as Marketingcamp, SEOday, Shopcamp, Digital Marketing, E-commerce Manager, Ecommerce Day, Web Analytics Wednesday and many more.