Higgins was looking at videos coming out of the Daraya region when he noticed several weapons that he had not yet documented in Syria, among them a portable anti-tank rocket and a wheel-mounted recoilless rifle.

Source- New Yorker https://www.newyorker.com/magazine/2013/11/25/rocket-man-2

It seems to me that the entire phrase is modifying weapons.

So the phrase has a noun and Among them --prepositional phrase . what does that make it?

Higgins was looking at videos coming out of the Daraya region when he noticed several weapons that he had not yet documented in Syria, among them a portable anti-tank rocket and a wheel-mounted recoilless rifle.

Source- New Yorker https://www.newyorker.com/magazine/2013/11/25/rocket-man-2

It seems to me that the entire noun phrase is modifying weapons. So it cant be an absolute phrase.

Isn't a noun phrase modifying another noun an appositive

Higgins was looking at videos coming out of the Daraya region when he noticed several weapons that he had not yet documented in Syria, among them a portable anti-tank rocket and a wheel-mounted recoilless rifle.

Higgins was looking at videos coming out of the Daraya region when he noticed several weapons that he had not yet documented in Syria, among them a portable anti-tank rocket and a wheel-mounted recoilless rifle.

Source- New Yorker https://www.newyorker.com/magazine/2013/11/25/rocket-man-2

It seems to me that the entire phrase is modifying weapons.

So the phrase has a noun and Among them --prepositional phrase . what does that make it?