Your LED -phototransistor should equally well operate with a "DC" light, or, modulated by pulses with 100 Hz up to 40 kHz for a larger distance if needed.
If you happen to get a device like the phototransistor and not know the connections, use an ohmmeter to see between which pins and with what polarity the device changes its resistance when lit or not lit from the IR LED.
Phototransistors are handled like regular transistors; biasing the base allows for a better sensitivity. You can also combine your IR LED with another photodiode; many are sensitive to IR light, too.