I can only assume no butter/milk.
Vegan mashed potatoes have been a struggle of mine for years. Soy milk and veggie oils simply don't whip as well as dairy milk/butter. One thing I've found to help a lot is use smaller potatoes.
I've found using red potatoes instead of the traditional Yukon Gold or Russet to be a bit better. They're less starchy and mash better on their own. You'll never get the traditional creamy potatoes, but they still go down easier than the ol' vegan potato brick.
Also, since you're not using gravy, I've found boiling the potatoes in a vegetable broth adds flavor--I usually go half water, half broth. And some garlic, green onion or shallot, and kale mixed in is really yummy.