Change font size in project file tree in PHPStorm
Font in the tree was not configurable in older versions. In the recent versions it should work using the configuration in Settings | Appearance.
To change the editor font use the Save As... button as you can't modify the default scheme.
For 2017/2018 versions of PHPStorm it's under menu item PHPStorm > Preferences > Appearance & Behaviour > Apperance > Override default fonts by. Here you can change the font and the font size.