A phrase to describe the idea of 'high literature'?

The classics may suggest the idea of high literature:

• (Literary & Literary Critical Terms) the classics a body of literature regarded as great or lasting, esp that of ancient Greece or Rome. (Collins)

• A classic is a book accepted as being exemplary or noteworthy, for example through an imprimatur such as being listed in a list of great books, or through a reader's own personal opinion. Although the term is often associated with the Western canon, it can be applied to works of literature from all traditions, such as the Chinese classics or the Indian Vedas. (Wikipedia)

• He only reads the classics.

For some, it's

literary fiction

Literary fiction is a term principally used for certain fictional works that hold literary merit. In other words, they are works that offer deliberate commentary on larger social issues, political issues, or focus on the individual to explore some part of the human condition. Literary fiction is deliberately written in dialogue with existing works created with the above aims in mind. Literary fiction is focused more on themes than on plot.

Literary fiction is usually contrasted with paraliterary fiction (e.g., popular, commercial, or genre fiction). This contrast between these two subsets of fiction is highly controversial amongst critics and scholars who study literature.

Wikipedia

I think this question has many easy answers in informal contexts. By way of example,

He doesn't read Tom Clancy: he only reads high-brow books.

I disagreed with her about whether or not that novella qualified as serious literature.

We love Game of Thrones but don't really think of the books as really deep literature.

All of these sentences are various levels of informal, and the last one is something which someone might say but would be unlikely to write. They all also carry the desired meaning.

However, if you are writing in a formal context, I don't think there is a simple word or phrase that encapsulates this idea.

Depending on your needs, merely using the word "literature" may carry all of the connotations you desire. It lends a bit more gravitas than "book", which is a bit pedestrian by comparison. If you feel that the distinction is not sufficient, you might write "high-caliber literature".

substantive literature

This is an appropriate adjective for art, film, and literature. Moreover, it highlights Harry's reason; he may believe Tom Clancy books lack meaningful substance.

1. Highbrow literature / books / magazines / theatre etc.
2. Cerebral literature / books
3. Sophisticated literature / works
4. Scholarly works / editions
5. Erudite works / researches [erudite (adjective) - having or showing extensive scholarship; learned]

The aesthetic value of both literary and cinematographic works ranges from superficial entertainment to highly complex masterpieces, but the language has a special term art films for the films that are striving to be at the higher end of that scale, and no analogous term, such as art literature, for the comparable literary works. Why?

The answer is that the terms film and literature are anchored in the different parts of the scale of aesthetic merit. When one hears the terms film or movies, without any qualification, one is likely to think first of the typical products of the Hollywood studios. These are the films that are designed to be as commercially profitable as possible, by being entertaining and appealing to wide audiences, and that do not even attempt to achieve any artistic value that might get in the way of commercial success. Because this is the default for the concept of a film, we need a special term for the films that depart from the default, and art film, in some contexts, serves that purpose. On the other hand, the term literature is, for most people, anchored in the classics that they read as a part of their education. When they hear the word literature they first think of such works, which are of relatively high artistic value. We thus do not need any qualifier to add to literature in order to direct attention to the higher end of the scale of artistic merit, because the word literature does that by itself. In the case of literature, we do, however, need special terms, such as pulp fiction for the works at the lower end of the scale.

(This answer elaborates on what was first posted by FumbleFingers in a comment.)