More advanced soapmakers do NOT put a drop of phth on their bars. That is not the correct way to use it. Most soapmakers don't use it at all, by the way.
I'm interning in a chemical research role at a soap company at the moment and have to concur. Universal indicator pH paper is useful for a rough idea of what's going on, but the standard is to use a pH meter with a fischer electrode
(at least I think that's the correct standard, I'm not a work to check). There are two problems with the use of phph and litmus paper, as described by the OP:
1.) phph is itself acidic and small quantities are used in relatively large solutions to indicate pH qualitatively. A drop of phph on the surface of soap is too concentrated, and soap isn't a solution. You can dilute a small quantity of soap in water and then test with phph and extrapolate the average pH in the soap, if you like.
2.) Soap in its early stages is still doing a lot of reacting, and there is a pH differential in the areas where its reacting more quickly. Testing one part of the soap may be completely meaningless. Indicator strips are equally useless when it comes to this phenomenon.
There are different considerations depending on the process. Colgate Process made soaps (mass-produced) measure pH differently from how cold-process home-gamers might, and cold-process people are going to do it slightly different from hot-process people.
In general though, I think the biggest problem a lot of beginning soapers have is with patience. The process is slow. Let it happen.
Absolutely agree that a lot of the information about soap chemistry on the internet geared towards DIY/small business is garbage. Utter hateful trash. Not all of it, or most of it, but it's hard for laypeople and beginners to separate wheat from chaff.