Stop ERPNext from Saving "Phone" number to "Mobile" field?

The default behavior of ERPNext seems to be save whatever phone number is in the “Phone” field to the “Mobile” field if there is no number added by the user.

This is asinine, and results in phone numbers that are NOT mobile numbers being inserted into the “mobile” field, which can cause issues with SMS implementations.

Is there a way to stop ERPNext from doing this?