The Splinter of Loretta Hardwood Spear

I saw this unique and I can't comprehend how to deal damage with this weapon. Poison is scaled off of the initial damage dealt + multiple other factors, the weapon can only give a max of 10-20 phys damage, and no elemental damage. I don't understand how you're supposed to get damage. I have been getting at about 20 stacks and do negative damage with this weapon, due to my skills only being able to do 25 damage because it's only physical. An explanation would be greatly appreciated.

your damage comes from having a kajillion stacks of poison active at the same time.

Invest in poison magnitude and duration (mostly duration), attack speed, and flat phys damage increases on other gear.
There's also another unique that lets elemental damage add to poison.

The spear has a modifier that doesn't allow the players to do ele damage. i think the only way to get damage is mag and duration and i don't think there is enough. I was lvl 65 and couldn't get enough with at least 20, I had 0 damage.

How do you scale physical damage with a unique weapons ?