Hello Brickscatter,
Thanks for using the Apple Support Communities!
If your iPhone seemed to be listening and typing your words in to a message, it sounds like you have dictation enabled. You can disable that in Settings > General > Keyboards > Turn off "Enable Dictation".
As for deleting that unsent message, these steps can help with selecting and editing that:
1. To select text, do any of the following:
* Select a word: Double-tap with one finger.
* Select a paragraph: Triple-tap with one finger.
* Select a block of text: Double-tap and hold the first word in the block, then drag to the last word.
2. After selecting the text you want to revise, you can type, or tap the selection to see editing options:
* Cut: Tap Cut or pinch closed with three fingers two times.
* Copy: Tap Copy or pinch closed with three fingers.
* Paste: Tap Paste or pinch open with three fingers.
* Select All: Select all the text in the document.
* Replace: View suggested replacement text, or have Siri suggest alternative text.
* Format: Format the selected text.
* 
: View more options
You can find that info and more here: Select, cut, copy, and paste text on iPhone - Apple Support
Hope that helps!
