Hi brockharman,
welcome to the Apple (user-to-user) Community!
Re: "I say 'van' - phone types 'vin #'... and I say 'van' a lot.... "
"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."
So, seems you may be able to change vin# to van simply by typing ... once you do that a few times, you may find that you no longer need to correct it all the time.
Above is from Dictate text on iPhone - Apple Support for iOS 17
If you are using an earlier iOS version on your iPhone 13, you may want to open the article from the above link, and change the iOS version at the top (ie: for more accurate info. in your own situation.)
If changing dictated text by typing is not an option:
See: How to contact Apple for accessibility support - Apple Support
or
You may want to reach out through Apple's Accessibility Support Website (NB: You can "Get Support" (online chat / phone / email etc.) from the link at the bottom of their website:)
Accessibility Support - Official Apple Support
All the best :-)