Map on our website doesn't work on iPhone

First rule of computer problem-solving: don't use the phrase "it doesn't work". It's not helpful. Instead: What do you expect to happen? What happens instead? Can you give screenshots?

Here's what I'd do to debug:

• Connect an iPhone to a Mac. Open Safari on the Mac. Make sure the Develop menu is enabled.
• From the Develop menu, select "iPhone" (or whatever the phone is called) and the title of your page in the subsequent menu.
• The developer console will open for that window on your phone.
• Press Command-Option-R to reload the page.
• Make sure "Console" and "All" are selected, so you can see any errors that your page is outputting.

When I do this, I see the following errors:

• jQuery.Deferred exception: undefined is not an object (evaluating 'screenfull.raw.fullscreenchange')
• _createButton — Control.FullScreen.js:80
• TypeError: undefined is not an object (evaluating 'screenfull.raw.fullscreenchange')

So you've got a problem with the code in Control.FullScreen.js, i.e. the Leaflet full-screen control that you're using. There appear to be some reported issues with it on the iPhone: see https://github.com/Leaflet/Leaflet.fullscreen/issues . Try removing this plugin and trying again.

This is basic JavaScript debugging, not specific to OSM. If your developer doesn't know how to do this you should possibly get a new developer.