Beginner Gardening: Doctor, please! Sick Philodendron Congo Green!, 2 by RoseTonic

RoseTonic wrote:
I am a real beginner green thumb, so any advice will be appreciated!

New plant, potted about six weeks ago & fertilised with Osmocote Indoor Plant Fertiliser, at that time; only in the last week have I noticed the following deterioration...
There is one leaf turning yellow, one larger leaf going soft and dark brown.
This potted indoor plant sits on my bedside table, back of my bedroom away from windows, but is close to a wall and a bedside lamp.
The yellowing leaf is the closest to the lamp.
The browning/softening leaf is closest to the wall.
You may also be able to see some other interesting marks appearing on some of the other leaves too...


I have done a little reading on:
yellow = over watering
browning = cold shock

But what do you think?!
Thank you in advance!