An iPhone has a screen resolution and also a viewport resolution. For instance the iPhone 11 actual screen is resolution is 828 x 1792 pixels and its viewport size is 414 x 896 pixels. You can find that the browser decides to show a page at the actual resolution instead of the normal viewport size that you actually want.
To set it to use the viewport resolution add this to the head section of your page:
https://ibex.tech/cloud/css/responsive-css/stopping-zooming-to-<meta name="viewport" content="width=device-width, initial-scale=1">
USEFUL?
We benefit hugely from resources on the web so we decided we should try and give back some of our knowledge and resources to the community by opening up many of our company’s internal notes and libraries through mini sites like this. We hope you find the site helpful.
Please feel free to comment if you can add help to this page or point out issues and solutions you have found, but please note that we do not provide support on this site. If you need help with a problem please use one of the many online forums.