You wil need:
Food processor
1 bar laundry soap like Fels Naptha or Zote, or Ivory - Zote can be found in hispanic grocery stores
1 Box Borax - found in the laundry aisle
1 box Washing Soda or Oxi Clean, orBaking soda - (Washing Soda AKA soda ash AKA sodium carbonate available in some grocery stores made by Arm and Hammer or you may find it art supply stores in the dyeing section)
OPTIONAL- essential oil of your choice, I didnt do it but I think tea tree might be nice.

Some recipe considerations, there are many variations to be found online but I based mine on this here http://www.thegreenguide.org/article/diy/household

'''Powdered Laundry Detergent'''

# 1 Cup Grated Fels Naptha Soap
# 1/2 Cup Washing Soda
# 1/2 Cup Borax
# For light load, use 1 Tablespoon. For heavy or heavily soiled load, use 2 Tablespoons.

I adjusted for the fact that Zote is at least twice as big as a Fels Naptha bar, and personally if I'm going to make a mess I'd rather double or triple the recipe which still easily fit in the food processor, also I used baking soda AND oxi-clean instead of the washing soda, the reason being that I could not find the washing soda, and Oxi-clean is essentially the same thing but with added peroxide* which does add a mild bleaching action, should be "color safe" though. It is also my understanding that baking soda is similar to washing soda but half as alkaline, so using baking soda will give you a gentler blend.

*note don't try and make the liquid recipe behind the link with "oxi clean" because the peroxide will make the whole mess foam, that was what I originally tried -- and ended up with useless semi solid foamy spooge.

 

I used the ultra pink Zote laundry bar though the recipe called for Fels Naptha (or you could use Ivory), this is where I wonder if it's actually phosphate free, but look at the color! yummy pink shreds! you may want to cut the bar down a bit before stuffing it in and using the grating disk attachment.

The big shreds of the bar soap might not dissolve as is, so you will need to change to the chopping blade of your processor, and now is the time to add the powder to the bowl of the food processor and blend it till it is fine, and don't huff the particulate OK? it will feel and taste beyond gross.

Clothes came out great!
But not sure if ....

A. that Zote is phosphate free, and (EDIT: someone commented that phospahates have been illegalized anyway, havent fact checked that though)
B. the purchase of the oxy clean sure drove my cost up, next time I will find the Washing soda.

borax 3.59
baking soda .75
Zote .75
oxyclean 5.00
= 10.09
But since one or two little scoops are enough I estimate about 75 washes? so that comes out to .12 a wash, I guess even using oxi clean it's not so bad.