I haven't set the form to go live yet but in testing I have found that the "Phone" field does easily allow dupes to be submitted.
The field requests entering the phone in a specific format - (###)###-####.
If the user enters in that exact format, the validation does stop the dupe. However, if the user enters in a different format, ########## or ###-###-#### for example - the dupe is submitted and stored. Note that even when entering in the "non-approved" format, the entry in the db is converted to (###)###-####.
I have not seen this behavior from other fields.