I bought microSD reader off Amazon, which has two dongle ends, one USB type A for a computer, one Lightning, for my iPhone. According to the included instructions, it required me to download an app (from the Apple app store) to use on the the iPhone. I didn't trust the App, even with Apple's scans, so I ended up using it with my already-owned Camera Connection Kit (Lightning to USB Host) adapter just fine. The name of the app was something very similar, if not identical, to that name, which is what reminded me of it.
It seems fishy that the Apple provided Files app didn't recognized my SD card