Ya, exactly, so you’re not running the actual app on your phone, this is why I was asking. The ionic dev app, as stated in it’s docs (https://ionicframework.com/docs/pro/devapp/) only has certain plugins installed on it. Here’s a direct link to the plugins pre installed on it: https://ionicframework.com/docs/pro/view.html#plugin-support
If you need other plugins that aren’t on that list, you must actually build and run the app on your phone, not just serve your web code over the net into the dev app.