Deploying your application
PhpStorm assumes that all development, debugging, and testing is done on your computer and then the code is deployed to a production environment.
The reason to stick to this "local development - deployment" model lies in the way PhpStorm provides its coding assistance which includes code completion, code inspections & validations, code navigation, etc. All this functionality is based on the project files index which PhpStorm builds when the project is loaded and updates on the fly as you edit your code.
To provide efficient coding assistance, PhpStorm needs to re-index code fast, which requires fast access to project files. The latter can be ensured only for local files, that is, files that are stored on you hard disk and are accessible through the file system.
If you are new to deployment with PhpStorm, these tutorials may be helpful:
Watch this video to learn more on deployment in PhpStorm: