If you want water in the outer pot for humidity, put sand in it to keep your orchid pot up out of the water. Sitting in water will likely cause root rot. I can say that Phals can adjust to low humidity and do just fine, mine do! Chances are any humidity gained from letting it sit with water under it will just dissipate into the room anyway though. As you get the balance of watering and letting it dry out right, you will be well on your way to being able to grow Phals successfully.