Arduino light sensor
As long as the "5V" source going in to the phototransistor is truly no more than 5V, then you shouldn't need additional components to just get a reading. If it's the 5V pin from the Arduino itself, you'll be fine. Note that some power sources labeled "5V" may actually go higher than 5, in which case it may damage the Arduino. 

The analog inputs are high impedance, so there is no need to worry about too much current going in to them. 

That being said, as Bradman175 mentioned, the BJT may alter the analog pin's read value (slightly). Using a mosfet could help with that.