How to have arrows for moving the cursor up and down when writing text on iPhone?
The arrows you see in your screenshot move the cursor to the previous or next form input field, they do not navigate within a text field to go to previous or following lines. If you have a phone supporting 3D Touch, you can force press on the stock iOS keyboard to quickly move the cursor (the phone will vibrate and the letters will disappear, then the keyboard area acts like a touchpad to control the cursor). If your phone does not support 3D Touch, you double tap and keep your fingers on the screen on the second tap for the same effect.