There is no restriction on the type of code you put in a monorepo that runs Turborepo. However, if you want Turborepo to do anything in that PHP codebase, you need two things:

• You'll need your monorepo's package manager to recognize the workspace
• Your PHP "workspace" will need to include a package.json that has the scripts key with the tasks you want to run.

For example, if your repo looks like this:

apps/
|-- php-app
    |-- package.json
|-- nextjs-app
    |-- package.json
package.json
turbo.json

If you're generally using npm, the root package.json will declare workspace:

{
  // <rest of package.json omitted>
  "workspaces": [ "apps/*" ]
}

and apps/php-app/package.json will look like

{
  "name": "php-app",
  "scripts": {
    "build": "composer start" // I haven't worked too much with PHP , so this is just a guess
  }
}

and turbo.json, could then have a standard build task (as shown in docs).

Hope that helps!