J. D. Biersdorfer, New York Times, points out a variety of ways to do dictation on your iPhone:

Hold down the iPhone’s Home button (or say “Hey Siri” to wake up the software), say “Make a new note,” and then speak your thoughts — reciting the punctuation like “period” or “comma” aloud. The resulting note can be emailed, copied, pasted or shared with a compatible text app.

And:

In Settings, go to General and then to keyboard to find the Dictation option buried at the bottom of the screen. When the setting is enabled, a small microphone appears on the keyboard of text-entering apps like Notes, Google Docs, Microsoft Word for iOS, or Apple’s own Pages word processor.

That setting is off by default. Check it. Good to know where this is.

Of course, you can also use a variety of apps to do dictation. J. D. highlights a few. Good stuff.