Try creating a static list of contacts those you would like to clear and update, set up a workflow to clear the property value for those contacts. Afterward, reupload a corrected list with the updated mobile numbers and HubSpot will automatically update them.
There should be a HubSpot workflow action that lets you clear out specific HubSpot values like this phone number depending on the triggers that you pick for a workflow
Try creating a static list of contacts those you would like to clear and update, set up a workflow to clear the property value for those contacts. Afterward, reupload a corrected list with the updated mobile numbers and HubSpot will automatically update them.