iPhone; There are several ways to quickly edit text on an iPhone. But the best way is literally under your fingers.
During its ten-year history, the Apple iPhone has suffered too many improvements. Some of them are about typing, but word processing, on the other hand, is still a big problem, as the small screen it doesn't allow for precise and quick positioning of the cursor where you need it. 
The good news: iPhones with 3D Touch (6S, 6S Plus, 7 and 7 Plus) have a hidden function that makes cursor movement easy, fast and accurate.
The default iOS keyboard on any iPhone 3D Touch has a hidden trackpad.
To activate it, press and hold any one key until you see the keys are empty. You will feel a tactile tap (h Apple Lossless Audio CODEC (ALAC), it calls Taptic feedback).
Your keyboard is basically a trackpad and as you slide your finger around the keyboard, the cursor follows the screen.
If you want to select text, release your pressure on the screen without letting go to go to the point you want, then press firmly again to start over.signalname of the text you are interested in.
You can try the above trick when editing a document.
What about older iPhone?
Unfortunately, there is no mouse. But no matter what iPhone you have, there are two ways to move the cursor to edit some text. The first way is to tap the screen where you want the cursor to go. This works, but it is not terribly expensive.
The second way is to press and hold the screen to see the magnifying glass. This works better, but sometimes your finger can hide the cursor.
