Single phase appliance on 3-phase circuit
You have not shared the voltage levels, so it makes it hard to answer perfectly, thing is you have two options to single phase... if you somehow got access to neutral, you can take a phase and neutral and connect to that. Neutral and ground are different.

The other option you have is the voltage of your fridge allows it is to take the voltage between two of the phases of your three phase system and use that as a single phase, this is higher than the phase to neutral voltage by about 1.7 times (square root of 3).

Once you know which option you can do &mdash; phase to neutral or between phases &mdash; the next thing you gotta do is calculate the current for the power rating of the fridge and see if your cables can handle that, on top of the current of whatever else is connected to it.

If you can please post more info of the fridge (what voltage is written on it) and what voltage your 3-phase system is, better advice can be given.