You can use external tools to handle this. Check launchpoint. Probably better handled in SFDC.
This may not work in every scenario (depending on the size of your database), but you can:
- Export all leads into excel and delete blank phone number rows
- Order the phone number column from largest to smallest
- Use Conditional formatting>Highlight Cells Rules>Duplicate Values
- Use Filter>Filter by color to show only the duplicate values
This will give you a view of all duplicate phone numbers in one place before deciding how to handle in Marketo/Salesforce. One potential issue is that many different leads may be using the same company phone number.
... one potential issue is that many different leads may be using the same company phone number.
+1, sharing a phone number isn't grounds for merging when Email is different!