Hello Fenway56,
Thank you for posting in the Apple Support Communities and for reviewing the related article Use the Health app on your iPhone or iPod touch. Getting an accurate reading for your steps is important, and we'd like to provide you with some tips that might help.
There might be some factors contributing to the varied step count from week to week, like your stride, or the way you're carrying your iPhone in your pocket. However, you can manually enter your steps in the Health app by tapping on Browse > Activity > Steps. The section "Add information about your health" in the related article above has a visual guide.
From there, consider whether steps was ever consistent from week to week after the same walk in the past. If so, there are a couple steps you can take to isolate the behavior even further. For instance, restarting your iPhone and ensuring it's fully updated are great ways to be sure that the device refreshes and has any current fixes. If an update is available, we recommend having a current back up of your data to iCloud or to a computer.
Restart your iPhone
How to back up your iPhone, iPad, and iPod touch
Update your iPhone, iPad, or iPod touch
If this concern continues after taking the steps above, our resolution is to contact Apple Support directly. Depending on your region, you may be able to reach them here:
Contacts Apple Support
We hope this information is useful. Kind regards.