If you didn't set up bounce rules in phpList, you can still find most of the email addresses of the bounced emails by exporting the mailbox of the bounce folder and then opening it up in TextWrangler.
Open MBOX file in TextWrangler →
Search: X-ListMember →
Find All →
Copy to new TextWrangler doc →
Save as txt →
Import into Excel
Data →
Get External Data →
Import Text File →
Delimited →
Other [:]
Then copy the email column and paste into TextWrangler, clean up (sort, delete duplicates). Copy/paste emails into phpList "Mass remove email addresses" (check box to also add the emails to the blacklist )
https://example.com/phplist/admin/?page=mass remove
UPDATE 9/29/20
Open MBOX file in BBEdit →
Search: X-ListMember →
Find All →
Copy to new BBEdit doc →
Save as txt →
Import into Apple Numbers and select email column
UPDATE 8/20/23
Even faster to just go straight from BBEdit to an email extractor and skip the text file altogether!