In NetBeans we can show detailed infos about declarations if we hold CTRL and hover the mouse over the function name.
How does this work in PhpStorm? I only get few infos on PhpStorm:
I only get more infos if I click on the function link in the yellow box which you can see in the screenshot.
In general -- just place caret on the element you are interested in (function/class/identifier/ect) and invoke View | Quick Documentation
(Ctrl + Q using Default keymap).
https://www.jetbrains.com/help/phpstorm/2016.3/viewing-inline-documentation.html
If you want this documentation window to be always visible -- just pin it (using Pin icon in top right corner). It will show the info on most recently invoked element.
If you want this info to be automatically updated for the element that is currently focused (based on caret position) -- activate Auto-update from Source
option there.
If you want this documentation window to appear automatically on mouse hover -- activate Settings/Preferences | Editor | General --> Show quick documentation on mouse move
option (delay is configurable).