Telefon je úplně nový.

Czech does not have articles, so there is no direct equivalent of the or a/an.

So Telefon je úplně nový can mean:

• The phone is completely new
• A phone is completely new
• That phone is completely new

Which meaning is intended depends on context. If Czech speakers want to make it more specific, they can add words like ten (that/the in many contexts):
Ten telefon je úplně nový.

Je means is. It is the 3rd person singular form of být (to be).

So:

• já jsem = I am
• ty jsi = you are
• on/ona/ono je = he/she/it is

In Telefon je úplně nový, je links the subject telefon with the description úplně nový.

Nový is an adjective meaning new, and its ending changes to match the noun it describes.

Here, telefon is:

• masculine
• singular
• nominative

So the adjective also appears in the masculine singular nominative form: nový.

Compare:

• nový telefon = a new phone (masculine)
• nová kniha = a new book (feminine)
• nové auto = a new car (neuter)

Yes, telefon is masculine, specifically masculine inanimate.

A useful clue is that many Czech nouns ending in a consonant are masculine. Since telefon ends in a consonant, learners will often correctly guess it is masculine.

That matters because adjectives and some other words have to agree with it:

• ten telefon
• nový telefon

Because it is inanimate, it behaves differently from masculine animate nouns in some cases, but in this sentence you only need to know that it is masculine singular nominative.

Úplně usually means completely, entirely, or in everyday speech often totally/really.

So Telefon je úplně nový is something like:

• The phone is completely new
• The phone is brand new
• The phone is totally new

In casual Czech, úplně is very common and can sometimes feel a bit broader or more conversational than a literal English completely.

Adjectives usually come before nouns when they directly modify them:

• nový telefon = a new phone

But in this sentence, nový is not directly attached to the noun inside one noun phrase. Instead, it is part of the predicate after je:

• Telefon je nový = The phone is new

So:

• nový telefon = a new phone
• telefon je nový = the phone is new

This is the same basic difference as in English.

Yes. Telefon je nový is perfectly natural and simply means The phone is new.

Adding úplně strengthens the idea:

• Telefon je nový. = The phone is new.
• Telefon je úplně nový. = The phone is completely / totally / brand new.

So úplně is optional, depending on how strong you want the statement to sound.

Telefon is in the nominative singular because it is the subject of the sentence.

Nový is also in the nominative singular masculine. After být (to be), Czech often uses an adjective in the nominative to describe the subject:

• Telefon je nový.
• Dům je velký.
• Kniha je zajímavá.

So both the noun and the adjective match in gender, number, and case here.

Yes, Czech word order is flexible, although the basic neutral order here is:

• Telefon je úplně nový.

Other orders are possible, but they change emphasis:

• Úplně nový je ten telefon. = emphasizes completely new
• Nový je ten telefon. = emphasizes new
• Ten telefon je úplně nový. = makes the phone more specific

For learners, the given order is the safest and most neutral.

A rough pronunciation guide is:

TEH-leh-fon yeh OO-pl-nyeh NO-vee

A few helpful notes:

• je sounds roughly like ye
• ú is a long vowel
• ě in úplně creates a nye-like sound here
• ý is a long ee sound

Also, Czech stress is usually on the first syllable of each word:

• TElefon
• je
• Úplně
• NOvý

Yes. These are all possible, but they feel slightly different in style:

• úplně nový = very common, everyday, natural
• zcela nový = entirely/completely new, a bit more formal or careful
• naprosto nový = absolutely new, stronger emphasis

So your sentence is very natural in ordinary speech:

• Telefon je úplně nový.

Yes. In real spoken Czech, úplně is often used very broadly, sometimes almost like:

• really
• totally
• just
• quite

So even though the literal meaning is completely, in conversation it does not always need to sound mathematically exact. In this sentence, though, learners can safely understand it as a strong intensifier: completely/totally new or simply brand new.