Requested feature overview description.
It is currently impossible to reorder posts in a pool using the "Order Pool" feature on a mobile since it requires dragging and dropping. A substitute, like "Move up"/"Move down"* buttons next to every post would be nice since it's a very handy feature on desktops.

For example, login and try to move the posts around at https://e621.net/pools/13645/order/edit on your mobile.

*Posts are listed in a single column due to the narrow device width, hence the "up" and "down".

Why would it be useful?
It makes it easier for people who are mostly browsing this site on their mobiles (myself included).

What part(s) of the site page(s) are affected?
The "Order Pool" interface. Nowhere else.