WillC said:The yellow patches indicate under watering. Indoor plants are non-seasonal so watering by the calendar can lead to problems. Many indoor plants need water more frequently in the dry winter air. I suggest that you water your Philodendron whenever the top half-inch of soil feels dry to the touch. Always water thoroughly. Under watering may be why the newer leaves haven't opened properly.
The lower leaves will never be replaced. The newer top growth looks healthy, so pruning and propagating it may be a good idea. I suggest cutting the top section just above the highest discolored leaf. That top cutting can be propagated by inserting it in the base of the existing plant or in its own smaller pot.
I also suggest making a second pruning cut a few inches above the soil. That will eliminate the entire middle section. New growth will emerge on the pruned stem starting a few inches above the soil and grow upward from there.
It looks like there is already a smaller stem at the base. You could end up with three separate stems in the same pot so you will have a much fuller looking plant.
WillC said:It is really hard to determine how much light is blocked by the opaque glass used in your bathroom. It is probably minimally adequate but less than ideal. Do you have a somewhat brighter option with light coming through clear glass?