Bryant, I've seen something like this before, but I don't remember if it's the same. Check if on the SFDC side, especially on the Marketo sync user if there's a special formatting requirement for the phone number field that would prevent the leads from syncing over I remember that some of our leads wouldn't sync over to SFDC because the phone number can't be blank or it must be formatted in a way that it has the +1 then area code etc. I remember that our SFDC administrator removed that restriction on our Marketo sync user, and after that the leads synced over to SFDC.