I believe you already know that this field uses the same logic as Web Form. But you forgot to go check web form before asking this question: Let me help you out.
(Just because you posted your installer *and* vicidial, both with version and with the vicidial build!)
Web Form -This is where you can set the custom web page that will be opened when the user clicks on the WEB FORM button. To customize the query string after the web form, simply begin the web form with VAR and then the URL that you want to use, replacing the variables with the variable names that you want to use --A--phone_number--B-- just like in the SCRIPTS tab section. If you want to use custom fields in a web form address, you need to add
&CF_uses_custom_fields=Y as part of your URL.
Now, I haven't tested this personally, recently, but I'm pretty sure this will work.