Electrical – How to simulate a phototransistor in a circuit, prefereably in ltSpice

The easiest approach is to use logic-level output photointerrupter like this one. There is no need for two power supplies, connect the transmitter side through a dropper resistor to set IR LED current (usually 50mA at 1.2V).

Output of this particular series is open collector, so if your load draws less than 50 mA,you can connect it directly between output and power source. For greater currents, add a PNP power transistor like BD136 on high side.

The output transistor has to be PNP because the photointerrupter output can only sink current (although it has a weak pull-up built in).

Edit: new schematic for split supplies

No way this could work reliably with single AA which can be anywhere between 1.6 and 0.9 Volts - there would be no margin for current regulation.

The pull-up resistor from your schematic is not needed since you need to amplify current and not to sense voltage.

You could consider adding a diode as shown below:

This approach can be made to work in particular if the IR level sensing you are doing is "digital" in nature. The lower drop of a BAT54 may be desirable.

If you are trying to actually measure analogue variation of the IR signal a more complex circuit may be required.