Using your iPhone as a Pen Drive can be a useful option in certain circumstances when you need to transfer large files and don't have access to the cloud or an internet connection. There are a few different methods you can use to do this, depending on the type of device you are transferring the files to.
One of the easiest ways to transfer large files to your iPhone is through AirDrop. This feature is only available on Mac devices, but it allows you to easily send files wirelessly to your iPhone. To use AirDrop, make sure your iPhone's reception is set to "All," and then use the Files app on your iPhone to save the transferred content to your device.
If you need to transfer large files to your iPhone from a Windows PC, you'll need to use a third-party file management app like Documents, Files Go, or iFiles. First, connect your iPhone to your PC using a cable and open iTunes. You'll need to trust the computer on both the PC and the iPhone. Then, go to the Files tab in the iTunes synchronization section and use the app to manage the content on your iPhone. You can drag files onto the app to transfer them to your device, or drag them from the app to your PC to transfer them the other way.
While it's not the most common use for an iPhone, using it as a Pen Drive can be a handy option when you need to move large files and don't have any other options. Just keep in mind to save the files to your iPhone's storage, rather than the cloud, to avoid using up your mobile data and battery.