Create nested folders or make sub folders in iPhone, mean having a folder inside another folder. Creating a folder in iPhone is as easy as dragging and dropping an app's icon in to another icon. But if you do this method for 2 folders, it won't be nested.
To create nested folders in iPhone, iPad and iPod Touch devices running iOS 9.x and later, do as follows:
1. Make sure you already have created 2 folders: Folder A and Folder B. And we are going to put Folder B inside the Folder A.
2. Drag and drop Folder A to the top of your screen (first Row)
3. Now starting holding your finger on Folder B, so it starts to wiggle.
4. Make sure you are still holding your finger on Folder B, and in the mean time, start tapping Folder A.
Important Note: You must tap the space between the top of Folder A and bottom of the Notification Bar
5. After tapping for about 5,6 times, Folder A should open and since you are holding Folder B you can easily move Folder B in to the Folder A by dropping it in to Folder A.