Thanks for your time, Stacy!
I put in a ticket with Synthesis and this was their response:
For security and site stability reasons, we have removed the WordPress editor system wide.
Editing PHP through WordPress is a very risky process, as a single character out of place can down your entire website. We encourage all users to edit PHP through SFTP, as you can use SFTP and a text editor to achieve the same editing goals in a much safer fashion. We also highly encourage backing up or making a copy of any files that you edit so you can easily undo changes should issues occur.
Here is more information on FTP and editing:
You can read our FTP Quick Guide for step-by-step instructions on how to connect and edit files via FTP here: https://websynthesis.com/ftp-connect-and-edit/
Be sure to use the SFTP protocol and port 2200. This will provide a much safer connection to your server, and will protect your files during transmission.
To avoid any confusion, below are the terms you will see in the screenshots and their equivalents in your Synthesis Customer Portal.
Server = FTP Domain
Username = sFTP User ID
Password = sFTP Password
