Is this a phosphorus deficiency?

Yes, last stage of P deficiency Also problem with Ca

Overwatering is causing the nutrient issue. The claws are a sign of to much nitrogen but with the leaves being light colored, I'm assuming you're over watering and the nutrients are leaching

Good Evening Mr.HH From the pictures and your description, it doesn’t look like a classic phosphorus deficiency. With phosphorus issues, leaves usually turn dark, sometimes with a purple or bluish tint, and necrotic spots spread from the edges inward. In your case, the damage looks more like a mix of nutrient imbalance (possibly potassium deficiency or pH-related lockout) and some light stress, since you mentioned many leaves are pointing upwards. I’d recommend Check your pH of both the nutrient solution and runoff often deficiencies are not from lack of nutrients, but from pH blocking their uptake. Check potassium (K) levels burned edges and spotting often point to K deficiency rather than phosphorus. Review watering routine irregular watering can worsen nutrient uptake. Light height even at 50%, make sure your Spider Farmer isn’t too close. Leaves pointing straight up can mean they’re reaching for light or reacting to too much intensity. In short: before adding extra phosphorus, double check pH and overall feeding plan. Often it’s not about “more nutrients” but correcting balance and uptake