Hmm if it is a phosphorus problem I'd say it is very minor when compared to searches online. Was hoping some others would chime in with their thoughts as well. I'm still figuring alot of this out myself but I've been learning reading watching vids etc for about a year now lol. My other two thoughts would be since you are outside and some strains are harder than others even down to the thickness it could have something to do with that. If you have dew on the leaves in the morning it could be magnifying the sunlight essentially burning/bleaching them which could explain the speckles on the leaves. My other thought could possibly be and early onset of leaf septoria. Leaf septoria can destroy foliage, stunt their growth, and affect the size and quality of the plant yields, but idk how common that is. Hopefully this helps you.