If the slope in the plot distance and time is steeper, so you think the speed of the motion is increasing or decreasing?

Depends on the way its "sloping"

If it starts left and goes right it's getting higher so its faster

If it starts right and goes left it has a negative association so it's slowing down

But if its steeper yes, because it's going up more at a faster rate the more straight up the slant is.