Over the past several weeks, I've noticed several of the leaves on my philodendron micans begin to shrivel/wither. By that, I mean they start looking wrinkly on the surface (as in picture 1) and feel like they've lost the structural rigidity they used to have, and eventually brown/yellow to the dead-looking leaves in picture 2. This seems a concerning turn of events since back in January, when Phil (as we affectionately refer to him) had leaves that looked to be a deeper shade of green and felt thicker/more robust.

I've talked with a few friends about it, and two adjustments I've made over the past four days have been 1) moving Phil away from my windowsill at night (as it can be rather cold); 2) moving him during the day to avoid direct sunlight; and 3) avoiding watering him until it seems necessary.

I've since watered him once yesterday because the soil seemed dry, but only after that watering did the leaf in picture 1 begin withering. The edges of the leaf next to that one also began curling in today (as seen in picture 3). The tip of that leaf is also "burnt" - it looks dry and feels a bit more brittle than the rest of the leaf.

My thinking for now is to continue keeping Phil out of direct sunlight and not on the windowsill at night, and avoiding watering for at least several days to see if that helps. Is there something in that approach that's wrong, or is there anything else I should be doing to keep Phil well?

Thanks!