Red phosphorus is not reacting with water.
White phosphorous does, but it needs alcaline environment.

OK, I don't remember the shift of water in CDCl3 correctly. The next step is a condensation or? I don't think this polymer will cause much trouble, your molecule is very acidic, and the base will pick the protons from this, not from the polymer. Yes, of course, you almost got rid of it, that's good.

What's with the 1s³... etc. when it says n begins at 3?

There are a number of UV-protective fabrics on the market. Whether or not they have been evaluated for your intended purpose, I do not know. They certainly cannot hurt. But honestly the the best way to protect plastics from photoinduced damage is just to keep them in the dark to the extent possible. Glass windows also block most of the harder UV rays from the sun, so diffuse/scattered/indirect sunlight in most inside areas will not noticeably degrade plastics over meaningful timescales.

I'm not really sure what you're hoping for here, but plastic components in consumer products should be OK for years as long as you're not keeping them under a black light or on a windowsill in direct beating sunlight for hours every day. My Nintendo GameCube has been stored in a dark closet for 25(?) years and it still looks and works fine.

The bigger point is that you can never protect anything 100% from degradation - even if you could make a barrier 100% impenetrable to UV light, there are still enough trace levels of ozone, atmospheric free radicals, and radioactivity sources (radon, potassium, uranium) hanging around that ensure that slow chemical degradation of everything (including humans) is inevitable. There's a guy who comes back here every few months fretting about the longevity of a diamond ring that holds some sentimental value to him. Can we calculate how long it will last? Are you sure it will not oxidize? How can I protect it? And you are not the first person who has dropped by stressing over degradation of high value electronics components. The fact is that unless you abuse these things, they will last a long time. Even so: Diamonds oxidize, polymers degrade, people get cancer, stars runs out of fuel, and the universe will die a slow, depressing heat death. Entropy always wins.

I would call our purification a partial success.  When there is a small amount of water present in CDCl₃, it usually shows up around 1.6 ppm.  I looked over the H-1 NMR of the starting material, and there is a low, broad peak that might be a polymer.  I am not sure whether I should ignore this signal in the starting material; I plan to buy some more of this starting material soon.