On Windows, most text editors support both "insert" and "overwrite" mode.
On the "insert" mode the caret is a vertical line and the characters you type are inserted at the caret position. On the "overwrite" mode, the caret is a block and the characters you type replace the characters at the cursor position.
You can switch between the two editing modes using the Insert key. The "insert" mode is the default.
PhpStorm can display a block caret in the "insert" mode. To enable this open application Settings then under Editor/General/Appearance check Use block caret.
I don't have a Windows computer at hand, I cannot tell if PhpStorm displays a line caret in the "overwrite" mode when the Use block caret is checked. :-(