| I'm more conservative on phal temps than hummer. I wouldn't let them get below about 15C. While it is normal for an old leaf to yellow and fall from time to time (phals often never have more than 4-5 leaves at a time), and it is normal for an old spike to die off, I suspect the low temps aren't helping your phal.
On the good side, if your roots are healthy and of you have figured out a watering regimine that works in your conditions, you're primed for success and have reason to be optimistic.
Maybe just consider keeping your phals warmer.
Happy Growing!
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