WPPluginWorks

Very lightweight and simple plugin that displays the currently installed PHP version in the “At a Glance” admin dashboard widget.

Current PHP Version

Know the currently installed PHP version in the "At a Glance" admin dashboard widget.

pedjas

Displays Apache and PHP version in footer of admin section for easy access.
These information are usually needed if reporting bugs or checking hosting service configuration. WordPress displays only it’s own version which is not enough.
Plugin is very simple and uses almost no resources. After all, it just displays version information.

Current PHP Version vs Show Apache and PHP version