I'm not sure what an "apposite phrase" is. The closest thing I can think of is an "appositive" - is that what you mean?

an appositive is a noun phrase that does not use a typical modifier intro - so it would not use "which" or any of those words to introduce the modifier. Here's an example:

The yellow dog, a Golden Retriever, is large.

"a Golden Retriever" is a modifier, describing the dog, and specifically it's an appositive - a simple noun phrase (no extra words) that describes another noun. "a Golden Retriever" is also what's called "non-essential" - meaning you don't have to have the words in the sentence to understand the basic meaning. The type of dog is just "extra" info.

In the example to which you linked (which we can't discuss directly anymore because it's an OG post from a long time ago), we had something like this (I'm substituting words):

A technique called Magic, which can make gold out of other objects, ...

We've got another appositive here, "called Magic," but in this case we aren't putting a comma between technique and Magic. Why not? Well, this time, "called Magic" is essential to the sentence - we're naming the technique. We're not just saying any technique can make gold out of other objects - we're saying that this technique is capable of making gold out of other objects.

The "which" part of the sentence, on the other hand, is NOT an appositive. The "which" refers technically to the "technique" (though you could say the full noun phrase is "a technique called Magic" not just "a technique"). The "called Magic" is an essential modifier that defines "technique" - so it's allowed to "get between" the main noun (technique) and the standard "which" noun modifier (which can make...).