Learn Hardcore Norwegian: Telefonen er den største distraksjonen min, og den ødelegger ofte konsentrasjonen. - The phone is my biggest distraction, and it often destroys my concentration.

Here you are talking about a specific, known phone (your phone in general), so Norwegian uses the definite form telefonen. This corresponds to English “the phone”, but instead of a separate word the, Norwegian uses the suffix -en.

What is the function of the first den in den største distraksjonen min?

In den største distraksjonen min, the den is linked to the superlative adjective største:

stor = big
større = bigger
størst = biggest
den største = the biggest

When a superlative adjective comes before a definite noun, Norwegian normally uses den / det / de in front of the adjective:

den største bilen = the biggest car
det høyeste huset = the tallest house
de viktigste oppgavene = the most important tasks

So den here is not “that” in the demonstrative sense; it is part of the phrase den største = the biggest / greatest.

Why is it distraksjonen min and not min distraksjon?

Norwegian allows two main placements of possessive pronouns:

pronoun before the noun (indefinite)
- min distraksjon = my distraction
- slightly more neutral, sometimes a bit more emphatic or contrastive
pronoun after the noun (definite)
- distraksjonen min = literally “the distraction my”
- very common in everyday Norwegian and often feels more natural

In this sentence, den største distraksjonen min sounds very natural and idiomatic.
You could say den største distraksjonen min or min største distraksjon:

den største distraksjonen min = “my biggest distraction” (focus a bit more on “biggest distraction of mine”)
min største distraksjon = also “my biggest distraction”, but word order feels a bit more like English and is somewhat more formal / stylistic here.

Both are grammatically correct, but the version with …distraksjonen min is very typical.

Why is the possessive min and not mi or mitt?

Possessive pronouns agree with the gender and number of the noun:

en (masculine) → min
ei (feminine) → mi (in Bokmål, many feminine nouns can also be treated as masculine and use min)
et (neuter) → mitt
plural → mine

The word distraksjon is masculine:
en distraksjon – distraksjonen

Therefore the correct possessive is min: distraksjonen min.

Could you drop min and just say Telefonen er den største distraksjonen?

Yes, you can. Both are grammatically correct:

Telefonen er den største distraksjonen min.
Telefonen er den største distraksjonen.

The version with min emphasizes that it is my biggest distraction specifically, a bit more personal.
Without min, it sounds a bit more general or objective: “The phone is the biggest distraction (in general).”

In actual use, the version with min makes it sound more like a personal confession.

Why is the second den used in og den ødelegger ofte konsentrasjonen instead of repeating telefonen?

The second den is a pronoun referring back to telefonen:

telefonen → den (third-person singular pronoun for common gender nouns)

In Bokmål, masculine and feminine nouns both use den as the pronoun:

en telefon → telefonen → den
ei bok / en bok → boka / boken → den

Norwegian often prefers to use a pronoun instead of repeating the noun, just like English:

“The phone is my biggest distraction, and it often ruins my concentration.”
Telefonen er den største distraksjonen min, og den ødelegger ofte konsentrasjonen.

Why is ødelegger used here, and does it always mean “destroy”?

Ødelegger is the present tense of å ødelegge, which literally means “to destroy / to ruin / to wreck”.

In this context, it is used somewhat metaphorically: the phone “ruins” your concentration, i.e. it breaks it, interrupts it, makes it impossible to maintain.

Examples:

Han ødela telefonen min. = He destroyed/ruined my phone.
Støyen ødelegger konsentrasjonen min. = The noise ruins my concentration.

So it can be literal (breaking something physically) or figurative (ruining a situation, mood, or in this case concentration).

Why is it konsentrasjonen and not just konsentrasjon at the end?

Again, this is the definite form:

konsentrasjon = concentration (indefinite)
konsentrasjonen = the concentration (definite)

Norwegian often uses a definite form where English uses a bare noun:

Jeg har mistet konsentrasjonen.
= “I have lost my concentration.”
Han trener opp konsentrasjonen.
= “He trains his concentration.”

So ødelegger ofte konsentrasjonen is naturally “often ruins (my) concentration”, where the definiteness in Norwegian covers what in English is often expressed by “my”.

Why is ofte placed between ødelegger and konsentrasjonen? Can its position change?

In den ødelegger ofte konsentrasjonen, the main word order is:

Subject: den
Verb: ødelegger
Mid-position adverb: ofte
Object: konsentrasjonen

This is the most neutral position for adverbs like ofte (often), alltid (always), aldri (never) in a main clause: after the verb, before the object.

You can change the position for emphasis or style:

Ofte ødelegger den konsentrasjonen.
→ Emphasis on ofte (“Often, it ruins the concentration.”)
Den ødelegger konsentrasjonen ofte.
→ Possible, but less typical; often sounds a bit marked or informal.

The standard, most natural word order is the one in the sentence: den ødelegger ofte konsentrasjonen.

Why is there a comma before og in ..., og den ødelegger ofte konsentrasjonen?

You have two main clauses:

Telefonen er den største distraksjonen min
den ødelegger ofte konsentrasjonen

Both have their own subject and verb, and they are joined by og (and). Norwegian comma rules allow (and often recommend) a comma between two independent clauses with different subjects, even when joined by og, especially if the clauses are not very short.

So:

Telefonen er den største distraksjonen min, og den ødelegger ofte konsentrasjonen.
= fully correct, clear separation of the two clauses

In everyday writing, some people might drop the comma:

Telefonen er den største distraksjonen min og den ødelegger ofte konsentrasjonen.

This is also commonly seen, but the version with the comma follows stricter style rules.

Is distraksjon always masculine, and what are its main forms?

Yes, distraksjon is treated as a masculine noun in Bokmål.

Main forms:

Indefinite singular: en distraksjon
Definite singular: distraksjonen
Indefinite plural: distraksjoner
Definite plural: distraksjonene

Examples:

Jeg trenger en distraksjon. = I need a distraction.
Dette er den største distraksjonen min. = This is my biggest distraction.
Alle disse distraksjonene gjør det vanskelig å jobbe. = All these distractions make it hard to work.

Could I say Telefonen er min største distraksjon instead? Does it change the meaning?

Yes, you can say:

Telefonen er min største distraksjon.

This is grammatically correct and has almost the same meaning: “The phone is my biggest distraction.”

Subtle differences:

Telefonen er den største distraksjonen min.
→ Focus slightly more on “the biggest distraction of mine”, feels very idiomatic and natural.
Telefonen er min største distraksjon.
→ Closer to English word order; can sound a bit more formal or written, depending on context.

Both are fine; your original sentence is very natural everyday Bokmål.