phash is sequential and single-threaded and like spaceyuck said, it’s also bottlenecked by IO, you’ll have to check your iowait to see if moving it locally would reap any benefits.
you can look towards this issue to add hardware acceleration, which increases the speed tremendously. Unfortunately it is also extremely fragile so I can’t offer much advice on how to implement it properly.
Alterantively, there are projets like darklyfter’s videohash node that will let you process off-device