@Ross Summerell , Welcome to Microsoft Q&A! Thanks for posting this question.
Adding to AnilSharma’s suggestions. Correct, you can build a PHP WebApp on App Service Linux.
In the same document(s) that you referenced there is a ‘Note’ which points to the doc for deployment on Linux OS.
Create a PHP app in App Service on Linux
Build a PHP and MySQL app in Azure App Service on Linux
You can also checkout the document for Readiness Checks and Migration Assistant.
We strive to make our Azure docs more discoverable and the docs aims at demonstrating key concepts with step-step instructions of a particular process /deployment and emphasis clearly with a ‘Note’ for any difference/distinguishes during the course. You may wish to know that you can always provide a doc ‘Feedback’ (for doc content improvements and enhancements) within that specific Azure doc. Much appreciate your feedback on this topic.