I want both my iPhone and Apple Watch to contribute to my step count

Most of my activity comes off my Apple Watch but I now have a treadmill at my desk and want the steps on that to count as well but my arm can't swing while working and I'm not moving anywhere so the GPS doesn't count any steps, but my phone in my pocket does seem to pick up the movement from my hips. I can see there is a larger step count on the phone data source in the Health app but it is not actually registering that in the Step count summary, it is only registering what my watch has recorded. How can I ensure the treadmill steps count and not just the ones registered by my watch. The data sources for Steps is first the watch and second the phone.

[Re-Titled by Moderator]