I sometimes need to carry files with me and transfer them from one computer to another. To do that I copy them to a flash drive. But then I leave that drive behind or lose it. Is there some way that I can use my iPhone for that kind of storage?
You can, though your iPhone won’t appear as a mounted USB hard drive as a normal flash drive does.
There are many iOS apps that will accept your files and then, via iTunes, let you copy them to another computer. TapMedia’s FileManager does this and it’s free. Just download a copy to your iPhone and then connect your phone to your Mac and launch iTunes.
In iTunes select your iPhone, click the Apps tab, and in the File Sharing area select FileManager. Drag the documents you want to store on your iPhone into the FileManager Documents area to the right. Unlike with some other apps, FileManager isn’t picky about what you throw at it. Although it can read some file types, if it can’t read a particular file it won’t refuse to store it.
Now unplug your iPhone and take it with you. When you later wish to retrieve one of these stored files, plug your iPhone into another computer, launch its copy of iTunes, and follow a similar process – select the iPhone in iTunes, choose the Apps tab, scroll down to the File Sharing area and select FileManager. Select all the files you want to copy to that computer and drag them to the desktop.
Before we leave the subject I might mention that moving files around this way is a little old-fashioned. Cloud services such as Dropbox, OneDrive, Google Drive, and, soon, iCloud Drive, let you place a heapin’ helpin’ of your files somewhere that’s easy to access (provided that you have an internet connection).