The method is quite simple, but there are still inconveniences. You need to install additional software on your computer - the iPhone folders explorer program. Once installed, it integrates into Windows and can work like a regular "Explorer". A jailbreak must be installed on your device and access to the file system must be opened using the AppSync utility from Cydia.
And so, in order for your device to be used as a flash drive, you need to:
1. Download and install iTunes from Apple.com.
2. Download and install the iPhoneFolders program on your computer.
4. Connect the i-device to the computer.
5. Go to My Computer / iPhone folders / Your i-device / private / var / mobile / and create a Temp folder (or another name). The path will turn out: My computer / iPhone folders / Your i-device / private / var / mobile / Temp
In order not to search for this folder every time, you can create a shortcut to the Temp folder and place it on your computer desktop. This will make it easier to access the iPhone's flash memory. Now, with the phone connected, you just need to click on the Temp shortcut and you are on the flash drive.