Is there a tool that can scrape form data (emails and phone numbers) from my site before it's submitted? If yes, when users drop out, can I retarget them?

Yes, if you are using the premium version of Gravity Forms Wordpress plugin this is a feature. It’s called partial entries. There are a couple other options that require more setup and code but this is by far the quickest.

As Robert suggests, an alternative solution to create a custom audience excluding the people that “converted” and including all people that visited this page. However, for this to work you would need to have a proper setup of for Facebook to capture the conversion data.