I am pretty certain the ARC PH-3 does not invert. as stated, manufacturers usually state if an item DOES invert, but usually do not mention if it does not.
The one company that had a lot of inverting stuff is Conrad Johnson, and they always mention it.
The reason for invert is EVERY stage inverts. Just some use only two or four stages, and a few, (like Conrad Johnson)uses three in some equipment.