Hmm new growth. Here is the thing. While the damage does look like phosphorous deficiency, the placement of the damage on the anubias (new leaves) does not make sense for phosphorous, and in fact does not match any new growth nutrient deficiencies.
This chart shows nutrients that are mobile/immobile/variably mobile and is extremely useful for diagnosing plant issues. Immobile nutrients are stuck in place wherever the plant used them. So when a deficiency in the water occurs the plant cannot salvage these nutrients and bring them to new growth. This means all the symptoms of the deficiency show up in new growth only.
Immobile nutrients are: Ca, Fe, B, Ni and Mn
Mobile nutrients are: N, P, K, and Mg.
Variably mobile nutrients: Cu, Zn, S, and Mo.
As you can see Immobile nutrients are
: Ca, Fe, B, Ni and Mn affect new growth. We can quickly eliminate Ni, Mn, and probably B since they don't show up very frequently (and in nickel's case never). As long as you are dosing plantex's CSM+B you are adding enough boron.
This leaves only iron and calcium, it isn't iron because you'd see new leaves begin to turn white, and you'd see this in other plants first. Anubias react slowly to nutrient damage. So it isn't iron. Calcium causes new leaves to grow in deformed, so it isn't this either.
After looking through the new growth nutrients we can see that it isn't any of them. Which makes a strong case for another problem being the cause of the damaged leaves.
I think this problem is likely damage from something. Without knowing more information, I'd guess it is probably from the excel or peroxide. If you frequently spot treat the anubias for algae then that is likely the reason.
Also, don't withhold phosphates, BBA will grow in your tank whatever the nutrients are in the water it isn't triggered by one specific mineral nutrient. There is some discussion/experimentation going on in an APC thread where we are investigating if BBA is related to high dissolved organics in the water. Basically the thinking goes - this is the reason you see it in petstores that have no nutrient addition and not very good lighting - because the water is full of dissolved organic wastes from 1000's of fish which promote its growth.
Can you post other photos of your other plants? There are no damaged leaves on any of them except the anubias?