Might depend on your micro-climate and where you have the orchid "outside" If you live in a dip (frost hollow) the temp might go below the predicted.....same if the plant is down near ground level. In any case the recommended low for Phalaenopsis is 55F....60F would be better. They are caspar milktoasts.

As Arthur indicates your microclimate makes a big difference. However, my general rule has been when the temps are forecasted into the 40's, one might wont hurt them. In fact I've left them for 2 week spans or more out and there was no ill effects.

Of course your mileage may vary. Mine are grown right up against the house on a covered porch. So again, see Arthur's comment about microclimates.

Of course, how could I have forgotten about microclimates! They are in a pretty well protected area away from any cold winds and have a tree canopy over top. But just to be safe I moved them into the greenhouse for the night which already felt much warmer than outside. I just hope I don't forget to take them back out tomorrow morning or they will definitely cook when the sun hits it.