L'antologia è disponibile in edizione tascabile.

Because antologia begins with a vowel, and the feminine singular definite article la is shortened to l' before a vowel.

So:

• la rivista
• la casa
• but l'antologia
• l'edizione

This is mainly for smoother pronunciation.

Antologia is feminine singular.

A very common clue is that nouns ending in -a are often feminine:

• la pagina
• la storia
• la biblioteca
• l'antologia

That is why the sentence uses:

• l' = feminine singular definite article
• è disponibile = referring to one thing, the anthology

È with an accent is the verb essere in the third person singular: is.

So:

• è = is
• e = and

The accent is important because it distinguishes two different words.

Examples:

• L'antologia è interessante. = The anthology is interesting.
• L'antologia e il romanzo = The anthology and the novel

Here disponibile means available.

In this sentence, it describes l'antologia, so it works like an adjective:

• L'antologia è disponibile. = The anthology is available.

Disponibile has the same form in masculine and feminine singular:

• Il libro è disponibile.
• La rivista è disponibile.

Its plural form is disponibili:

• I libri sono disponibili.
• Le riviste sono disponibili.

Italian often leaves out the article in expressions like this when talking about a format, category, or version.

So:

• in edizione tascabile = in paperback edition / in paperback format

This sounds natural and idiomatic in Italian.

You could sometimes see an article in other contexts, but here the article is normally omitted. The phrase is functioning almost like a set expression.

Similar patterns:

• in vendita = on sale
• in edizione limitata = in a limited edition / in limited edition
• in formato digitale = in digital format

Tascabile literally comes from tasca, meaning pocket.

So tascabile originally means something like pocket-sized, but in publishing it usually corresponds to paperback or pocket edition.

So edizione tascabile is a very common way to say:

• paperback edition
• sometimes pocket edition

Depending on context, English translators usually choose paperback.

The preposition in is used because the expression refers to the form or edition in which something is available.

So:

• disponibile in edizione tascabile = available in paperback edition
• disponibile in formato digitale = available in digital format

You can think of in here as meaning in the form of or in the version of.

In edizione tascabile, edizione is the noun and tascabile is an adjective.

• edizione = edition
• tascabile = paperback / pocket-sized

So literally it is:

• edition paperback/pocket-sized

Italian usually places many adjectives after the noun, which is why tascabile comes after edizione.

Yes, but the given word order is very natural and standard.

The sentence:

• L'antologia è disponibile in edizione tascabile.

is the most neutral way to say it.

You might also see variations for emphasis, such as:

• È disponibile in edizione tascabile.
  = It is available in paperback.

This works when the subject is already understood from context.

But if you are stating the full sentence clearly and neutrally, the original order is best.

No, not really. It is not a passive like is published or is sold.

The structure is:

• L'antologia = subject
• è = is
• disponibile = available
• in edizione tascabile = in paperback edition

So grammatically it is a normal copular sentence with essere + adjective.

You would need to change the article, the verb, and the adjective to plural:

• Le antologie sono disponibili in edizione tascabile.

Changes:

• l'antologia → le antologie
• è → sono
• disponibile → disponibili

The phrase in edizione tascabile stays the same.