Your original post asked, “What exactly is required for a PHd in (Christian) Theology?”
The answer is: specific requirements differ at various conferring institutions. In no case that I am aware of, however, does a conferring institution limit their study to the single command to read the Bible. This answers the critique you make in the rest of your post – the suggestion that because the entirety of the Bible is straightforward, it’s difficult to imagine a post-graduate course of study in theology.
Here is one example about which there is considerable scholastic disagreement: Jesus’ brothers.
The English translation of the Bible refers more than once to Jesus’ brothers. Matthew 12:55-56, for example, in the King James version, Jesus’ teaching in his home town causes onlookers to question his wisdom, apparently because they knew him as a child and know his family, and do not understand how he knows all the things he teaches: " Is not this the carpenter’s son? is not his mother called Mary? And his brethren, James, and Joses, and Simon, and Judas? And his sisters, are they not all with us? Whence then hath this man all these things?"
That translation seems to say clearly and plainly that Jesus had brothers and sisters – it even names his brothers. This is, as your original post suggests, something the average college freshman can easily understand.
However, it’s obvious that the Bible was not written in English. Jesus’ words did not even appear in red text. The language spoken at the time was Aramaic; the written language from which we derive our primary source information for the Bible was Greek. And there is some dispute over the meaning of the Greek words adelphos and adelphe. Literally they are translated as “brother” and “sister,” to be sure. But the literal translation of “raining cats and dogs” is that animals are falling from the sky. Translations must capture idiomatic meanings. The word is used in other contexts to mean something other than a literal sibling. Lot is Abraham’s “brother” according to Gen 14:14, even though the text makes clear he’s the son of Abraham’s actual sibling brother Haran – for which the literal English word is “nephew.” Neither Hebrew nor Aramaic had a distinct word for “cousin,” which explains Mali’s sons Kish and Eleazar’s offspring in 1 Chronicles 22: Eleazar died having fathered only daughters, who married their “brothers,” the sons of Kish. In fact, that describes a marriage of first cousins.
This is one example of Biblical scholarship that – in my view – extends beyond the ken of a college freshman, at least insofar as analysis and acceptance, or refutation, of the claim that Jesus had siblings. And this, in turn, gives lie to the thesis of the OP.