Cleaning System Cache
PhpStorm caches a great number of files, therefore the system cache may become overloaded. Sometimes the caches will never be needed again, for example, if you work with frequent short-term projects. Also, the only way to solve some conflicts is to clean out the cache.
From the main menu, select.
In the Invalidate Caches dialog, select the relevant action. You can invalidate the caches and restart the IDE, invalidate the caches without restarting the IDE, or just restart the IDE.
For details on where various user-specific files are stored, see Default IDE directories.