You have to have the phone plugged in via USB (no wireless charging connection or whatever) and then you’ll see the device in that same Develop menu. If you have a Mac, doing this is pretty similar to what we just did. And if you can run the iOS simulator, that means you can run desktop Safari as well, and thus even have access to DevTools that can reach into the simulator. I happen to have a Mac, so I can have XCode installed and thus have an iOS simulator that is pretty easy to pop open. Problem not showing here? Then the problem is actually unique to iOS Safari.
Now you’re actually using Safari, which is way closer to iOS Safari than desktop Chrome is. Does it seem actually specific to Safari? Lemme check Desktop Safari first since that’s just a few clicks away. Note that this does a smidge more than just display your site in a smaller area: it sends the correct User Agent String and Client Hints for that device. Lemme just use the device mode in Chrome quick. These are my general steps, starting with not even using iOS Safari.