From Apple ...
Dictate text on iPhone
With Dictation on iPhone, you can dictate text anywhere you can type it. You can also use typing and Dictation together—the keyboard stays open during Dictation so you can easily switch between voice and touch to enter text.
Dictation requests are processed on your device in many languages—no internet connection is required. When dictating in a search box, dictated text may be sent to the search provider in order to process the search.
Turn on Dictation
Go to Settings > General > Keyboard.
Turn on Enable Dictation. If a prompt appears, tap Enable Dictation.
Or, there’s always Dragon Dictation ...
Apple voice to text is awful
Southern accent
Forget it