Phototransistor with virtual ground opamp design
First of all the phototransistor seems to be drawn upside down, the emitter should be at the negative side. 

In your circuit, the inverting input is held at the virtual ground potential by the feedback loop. In order for the output of the opamp to be made to go positive, current must be drawn from the circuit node to which the inverting input is connected. This will cause the inverting input to tend to go negative and the output voltage will rise, causing current to flow (to the left) through the feedback components thereby restoring the voltage at the inverting input terminal. In order for this to happen the phototransistor must be connected to a more negative potential than the virtual earth. The "true ground" would be a suitable point. If it were returned to the virtual ground, then there would be no potential difference across the transistor and the circuit would not work.