From the original source:

The use of white phosphorus in Gaza, one of the most densely populated areas in the world, magnifies the risk to civilians and violates the international humanitarian law prohibition on putting civilians at unnecessary risk.

Upon contact, white phosphorus can burn people, thermally and chemically, down to the bone as it is highly soluble in fat and therefore in human flesh. White phosphorus fragments can exacerbate wounds even after treatment and can enter the bloodstream and cause multiple organ failure. Already dressed wounds can reignite when dressings are removed and the wounds are re-exposed to oxygen. Even relatively minor burns are often fatal. For survivors, extensive scarring tightens muscle tissue and creates physical disabilities. The trauma of the attack, the painful treatment that follows, and appearance-changing scars lead to psychological harm and social exclusion.

Attacks using air-delivered incendiary weapons in civilian areas are prohibited under Protocol III of the Convention on Conventional Weapons (CCW). While the protocol contains weaker restrictions for ground-launched incendiary weapons, all types of incendiary weapons produce horrific injuries. Protocol III applies only to weapons that are “primarily designed” to set fires or cause burns, and thus some countries believe it excludes certain multipurpose munitions with incendiary effects, notably those containing white phosphorus.

Human Rights Watch and many states have long called for closing these loopholes in Protocol III. Palestine joined Protocol III on January 5, 2015, and Lebanon on April 5, 2017, while Israel has not ratified it.

And for some context on exactly how fatal this might be in a place like Gaza…

We’re talking about place where urban areas are 4x as dense as Los Angeles. Where people are not in the most steady health to begin with, given that 90-95% of the water supply is unsuitable for consumption, over 75% are food-insecure, 50% suffering malnutrition, the median age is 18, and there is no electricity or fuel to power the hospitals and ambulances – not that it matters anyway, because even humanitarian aid facilities are being targeted by air strikes.

You could easily die from a small cut in Gaza. Anyone in the AoE here is totally fucked.