Designing a transistor switching circuit with opto-isolation
The PC817 has a CTR of 50% minimum at 5mA, it's about half that at 0.2mA so you can only count on about 50uA going to the base. You should also derate for aging and temperature, which makes it even worse, but let's ignore that for now.
That will support the transistor switching about 1mA with it well saturated (Ic/Ib = 20), which is about 1/300 of your desired load current.
I suggest boosting up the LED current to at least 5mA, and using a MOSFET rather than a wimpy little signal BJT. You can use the +12V supply (the PC817 is rated at 35V) so it does not have to be a logic-level MOSFET.