You need to repot your orchid. Your mix is to wet and broken down. You have moss growing on the near the edge of the pot. You have a little fertilizer (salt) burn but not to bad- the light brown splotches on top of your roots. To help reduce fertilizer burn when watering time comes water with plain water first to wet the roots and then fertilize. Personally I don't bother.
You write "I follow the weakly-weekly plan, but I think I haven't been putting enough emphasis on the "weakly" part :-)"
You kind of answer you question on fertilizing amount, though what one person considers weakly may be another persons strong or visa versa. Phals actually grow better with more fertilizer during active growth then your average orchid.
The below link to a cultural sheet is based on Dr. Yin-Tung Wang's research into growing Phals.

Here is a link that might be useful: Phal Care based on Dr. Yin-Tung Wang's research, Texas A&M University System

The only thing I would add to the great post above is to be careful with the cinnamon. It's great stuff for sealing off wounds but try not to get it on active roots. A small paint brush is what I use to put the cinnamon right where I want it.
Good Luck!
Pat.....

Remember, with the weekly weakly plan, every fourth watering should be a thorough flushing with plain water. Your plant also looks slightly over potted. You should use a pot that just accommodates the roots and a bit more.

Fertilizer burn is seen in the leaf tips more than it is seen in the roots. Phals having bigger tougher leaves than say an Oncidium might be harder to diagnose this way but looking at that picture I cannot see any sign of browning, none in the slightest. Therefore I don't think fert burn is the cause of any issues. Aerial roots are very prone to drying and shriveling especially in home conditions. I know the o.p. thinks light is great but for what its worth, I don't. It isn't awful, but it isn't great and that just might be the tipping point.

H

Also, your medium would have a very distinct ammonia smell if you have been using too much fertilizer.

Humph! I'd get this plant out of what ever it's growing in and pot it in a transparent pot of pure sphagnum. This is the way the Thais do it and I have never seen better orchids. Don't worry about overfertilizing. I give mine raw wood ash( K plus a bit of P) + a small amount of castor oil plant concentrate (N) 3 times a year and have never seen any signs of burn - I do water copiously however and find this mitigates a number of sins.

Thanks everyone for all the advice! I took the Phal on Friday to an orchid greenhouse and they repotted it for me -- into a mix of mostly coconut fiber with a few coconut chips, with solid foam chips in the bottom of the pot. It looks like . I was hoping for a coarser mix, but that's the only thing they had.

I suggested that the pot might be too big -- especially after seeing the root system! Let's just say there isn't a whole lot of it. But they didn't think so, and the pot stayed.

Oh well, at least all the roots are buried now. It was really depressing to see the root system in its full (un)glory: the parts of the roots that were buried were green and looked great, but the part where they emerge from the plant, which was exposed to the air, looked dried-out. I wonder if they're still functional like that?

"the parts of the roots that were buried were green and looked great, but the part where they emerge from the plant, which was exposed to the air, looked dried-out. I wonder if they're still functional like that?"

Aerial roots that go off like that are a sign of really poor humidity. It is quite common. It is usually harder to actually do something about the humidity than to keep the plants healthy in spite of it. Burying them of course gets them out of the dry air and into a zone of relative protection. They will never be as effective as roots in better shape but they are useful in their own way.

While the repotting was probably educational for you it is not the entire cure. The greenhouse that did the job gave you some home care instructions I hope. If not, the link posted in an earlier thread has at least some useful information. The first three points of care are the ones that matter most.

H