The WordPress Plugin for a signup form allows you to specify which fields to display on the form. If you select the Phone field, the plugin incorrectly maps this field to Mobile Phone rather than Home Phone. Address fields map correctly to Home address fields. When you create a landing page, Phone maps correctly to Home Phone.
This is a bug that should be fixed. The only work around is to go into each new contact and cut and paste the phone number into the correct location.
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I'm sorry for the inconvenience you have experienced with this problem. I have reported the problem to our team so they can take a look at this. If you should run into anything else, please feel free to reach out. Thank you for choosing Constant Contact, have a great day!