How to Enter a Backslash on an iPhone
Find both the backslash and forward slash keys on the iPhone or iPad's virtual keyboard, and maybe a few other keys you need along the way.
Launch the app that you want to type in and tap the screen to place the cursor. When the virtual keyboard appears, tap the 123 key to open the Numbers keyboard.
Tap the #+= key to open the Symbols keyboard. If you need a \, or Forward Slash, it's located on the Numbers keyboard here. A forward slash is commonly used in website URLs, such as http://www.sample.com/webpage.html.
Tap the \, or Backslash, key. To toggle back to the Main keyboard, tap the ABC key. To return to the Numbers keyboard, tap the 123 key.
University of South California lecturer, Phil Conrad, has a good way to distinguish a backslash from a forward slash. Picture someone walking past you, from left to right, in the same direction you type. Someone leaning backward resembles a backslash. Someone leaning forward looks like a forward slash.