You need an amplifier on the receiver, the photo-transistor isn't intended to be used on it's own, it's intended to feed a high gain amplifier. To get good range it can be quite complicated, it's usual to modulate the beam and only amplify the received modulation - this avoids problems with ambient light etc.
The usual modulation fequency is about 40KHz, and you can buy small three pin receiver IC's which do everything - simply providing a high or low output. These easily work at 10-20 metres. For the transmitter you could use a simple 555 oscillator.