Thanks for getting in touch! Our general rule of thumb is, if you can package into a supported package type, you can deploy with Octopus. In Octopus 3.3 we added support for ZIP files (check out our docs on creating ZIP packages), so you can package your PHP app into a ZIP file and run scripts to do what you need to do (including support for Bash).
Additionally, we have a great blog post written some time ago (before ZIP support was introduced) called Deploy a PHP site to IIS with Octopus. While it may not be exactly what you're doing, it may give you a good idea of the process used to deploy a non .NET app with Octopus. https://octopus.com/blog/deploy-php-to-iis-with-octopus
I hope these resources help. Feel free to reach out again if you have any further questions, or want to clarify your requirements and details on your environment, and I'll be more than happy to help you find the best solution.