I know this is probably really simple, but I have tried “total” and “sum” and can not figure out how to get it to work. I have this table entered from a function and I need to get the sum of the output column. How do I do that?

Similar to @Mike_Gleeson 's suggestion, if you name your first column x_1 and your second P(x_1), then you should be able to use the total function as total(P(x_1) ). This would work similarly with a list, x_1, and the defined function without a table.
I’m guessing you tried total(P(x)), but that essentially calculates the total at each evaluated x, which just outputs the original function. You need a list for x to get the desired result.
