Grounding a phonostage

Greeting to all,

This might sound like a noob question but I can't help but to wonder how a phonostage grounding really works.

Looking at the picture attached below, there is only a 2-pin wall wart power supply used to power this phonostage.
And the so-called "Ground" on the phonostage is mere physical contact to its casing only.

Saying this, do I need to connect additional piece of wire from phonostage to mains, in order to ground the phonostage properly (other than the ground wire from turntable to phonostage)?

Regards,
Leong

note your rca connector is also touching the case . thus grounding the case to the amp will ground all the case , the rca return . 
in fact once you plug the rca to the amp , all are already grounded. but if you provide a dedicated ground wire ( thicker cable) at he ground point will be sure better. 
some time , too many path of grounding will generate ground loop which will make thing bad . Hum sound.