Deploying a redirect.php?

I am following this guide...

https://www.jotform.com/help/213-Send-POST-Data-From-JotForm-Using-PHP-in-Custom-Thank-You-Page

I wanted to know how I would deploy the redirect.php page into my website. I am using weebly to make the website and wasn't able to figure out how to do it.

If you need to get your custom Thank You page with your custom .php file you will not be able to do it on Weebly, seems like they do not support custom side server code (PHP and others) as per this link: https://community.weebly.com/t5/Site-Editor/Is-it-possible-to-upload-a-custom-page/td-p/14873 

What I would suggest you is to store your .php file on another server so you have full access to it. 

Are there any other website building services that you would recommend in order to accomplish my goal? 

Website builders are very limited regarding to add custom PHP codes or JavaScript codes, but I think you should use WordPress for this, you can design your website and as far as I know it allows to customize it with custom codes (PHP, JavaScript, CSS), here is a link that I found about it: http://www.wpbeginner.com/wp-themes/how-to-create-a-custom-page-in-wordpress/