Hello,
Thank you for your question today. I am slightly confused as to the exact question. If you are looking for captcha for phplist, for wordpress, or for a phplist plugin that is integrated into wordpress.
Below are a couple of links that may assist with the phplist and wordpress options.
Forum topic on adding captcha to phplistWordpress phplist plugin
I could not locate anything for a captcha for a phplist plugin integrated into Wordpress. For that you may want to visit the Wordpress forums and see if someone may have an idea of a plugin that includes that.
Regards,
Scott M