Výše pojistného a pojistná částka jsou vysoké.

Because after výše meaning amount / level / extent, Czech normally uses the genitive.

So:

• pojistné = insurance premium
• výše pojistného = the amount of the premium

Here, pojistného is the genitive singular form.

In this sentence, it functions as a noun meaning insurance premium.

Historically, it comes from an adjective, and it still declines like one. This is very common in Czech: an adjective becomes a noun because the main noun is understood.

So you can think of pojistné as a substantivized adjective:

• nominative: pojistné
• genitive: pojistného

That is why its forms may look adjectival even though it is being used as a noun.

Here výše means amount, level, or extent in a formal or administrative style.

In financial language, výše + genitive is very common:

• výše platu = the level/amount of salary
• výše pokuty = the amount of the fine
• výše pojistného = the amount of the premium

Výška often refers more literally to height, although it can also sometimes mean amount. In insurance and formal writing, výše pojistného is the standard phrasing.

Because the sentence has two subjects joined by a:

• výše pojistného
• pojistná částka

Together they form a plural subject, so the verb must also be plural:

• jsou = are

If there were only one subject, you would use je:

• Pojistná částka je vysoká.
• Výše pojistného je vysoká.

Because vysoké agrees with the combined plural subject.

The two subject nouns are:

• výše — feminine singular
• částka — feminine singular

When two feminine singular nouns are joined by a, the result is plural. The predicate adjective must therefore also be plural.

So:

• singular feminine: vysoká
• plural feminine: vysoké

Compare:

• Pojistná částka je vysoká. = singular
• Výše pojistného a pojistná částka jsou vysoké. = plural

It is in the nominative singular.

That is because it is one of the subjects of the sentence. The subject in Czech is normally in the nominative.

So in the sentence:

• výše = nominative singular
• pojistného = genitive singular
• pojistná částka = nominative singular

Even though pojistná částka is singular by itself, the whole subject is plural because it is joined with another subject by a.

Because Czech has no articles.

English says:

• the premium
• the insured amount

Czech simply uses the noun without an article:

• pojistné
• pojistná částka

Whether something is the, a, or just a general concept is usually understood from context.

It is not completely fixed.

Czech word order is more flexible than English word order. You could also say:

• Pojistná částka a výše pojistného jsou vysoké.

This has essentially the same meaning. The original order sounds natural and fairly formal, but the alternative is also grammatical.

Word order in Czech often depends on emphasis and information structure, not only grammar.

No. Here it means high in the sense of large in amount.

Czech uses vysoký / vysoká / vysoké not only for physical height, but also for things like:

• prices
• fees
• salaries
• taxes
• insurance amounts

So vysoké is the normal word here, just like English uses high in high price or high costs.

Both are possible, but they are slightly different in style and focus.

• Pojistné je vysoké. = The premium is high.
• Výše pojistného je vysoká. = The amount/level of the premium is high.

Using výše pojistného sounds a bit more formal, precise, and administrative. It focuses specifically on the amount.

So in insurance, business, or legal language, výše pojistného is very natural.

They are related, but they do not mean the same thing.

• pojistné = the premium, the money paid for insurance
• pojistná částka = the insured amount, the sum insured
• pojistka = an insurance policy, or informally insurance; in another context it can also mean a fuse

So in this sentence:

• výše pojistného refers to how much you pay
• pojistná částka refers to how much is insured / covered

That distinction is important in insurance vocabulary.