I'll second this post. Really dirty chips may need a longer soak and/or hotter water and/or more TSP, but test out a chip or 2, to try and ensure the longer soak won't get water under inlays or damage hotstamps. And even water under inlays can evaporate over time, especially by putting the chips in front of a fan or blow dryer.
No. Either will work just as well to clean chips. (IIRC, I think the phosphate free is just more eco-friendly, reducing phosphate runoff from sewer discharge into rivers, bodies of water, etc.). The TSP cleaner is great on removing casino 'gunk' - it sort of 'melts' away.
I've cleaned thousands of chips with TSP solution, by hand & toothbrush (with bristles cut shorter). I later got an ultrasonic and have cleaned thousands more. One tip for the hand cleaning method, like moose, I'd do around 40 chips at a time in the cleaning solution, then I'd remove the chips by the barrel, place the still wet chips in a rack to align the edges of 20 chips in a barrel, and that way I can brush the sides of 20 chips at a time. Then I laid the chips individually out on a towel to brush the front, flip, then brush the back.
For a hotstamp chip that needs a good scrubbing, I read this tip on PCF somewhere, and cover up the hotstamp with your thumb (optionally wear a kitchen rubber glove on one hand, The glove just protects the skin of your thumb from the bristles and the TSP solution.), and brush around it. That way you can still brush hard to clear dirt out of the mold impressions on the edge of the chip, but limit damage to the hotstamp foil.