SFDC question here. I pulled a Contacts & Accounts report and brought in the account phone number and the contact phone number in the report. What's strange is that on the report, some contacts who do not have a phone number on the contact object have a contact phone number listed on the report that is the same as the account phone. Is it possible that since there is no value for the contact phone that it is somehow inheriting the value from the account phone?
Honestly, if it were doing that it'd need to be a workflow or formula of some kind, and you would see the result in the Contact record just by looking in the page layout as well. So if you can't see that, it's unlikely. Reports are just a reflection of the data in the field. It's more likely you have multiple "phone" fields and you've accidentally go one rather than the other showing in your report.
Salesforce reports are tricky to troubleshoot without actually seeing the report though.