PHPStorm is (in my opinion) the best PHP IDE out there. It is - like most IDEs - project based and therefore it's not possible to create a new temporary text file to paste content in (like you're used to in a text editor). Instead you have to create a new file and delete it afterwards. As that's to much trouble, most people still use a text editor for that.

But if you love PHPStorm like I do, you will miss all the functions like search and replace (in the PHPStorm way).

Fortunately there is a plugin for that called Scratch. With it you can hit a few shortcuts like Alt+C, Alt+C to open the default scratch (temporary text file), Alt+C, Alt+A to create a new scratch or Alt+C, Alt+S
to show a list of existing ones.

Those are just the default shortcuts (there are more) and of course you can change those in your keymap.