Simkortet sitter i telefonen.

Because Swedish often uses position verbs where English simply uses to be.

The main ones are:

• sitta = sit
• ligga = lie
• stå = stand

For something like a SIM card that is inserted/fitted into a slot, Swedish naturally uses sitta. So Simkortet sitter i telefonen sounds more idiomatic than using är.

In English, we usually just say The SIM card is in the phone, even though Swedish is being more specific.

Yes, people would understand it, and it is not grammatically wrong.

But sitter is more natural because it suggests that the SIM card is physically in place in the phone. Är is more general and less specific.

So:

• Simkortet sitter i telefonen = more idiomatic
• Simkortet är i telefonen = understandable, but less natural in this context

Because simkortet is the definite singular form, meaning the SIM card.

The basic noun is:

• ett simkort = a SIM card

Since simkort is an ett-word (a neuter noun), the definite ending is -et:

• ett simkort = a SIM card
• simkortet = the SIM card

So -et is doing the job that the would do in English.

For the same reason: telefonen is the definite singular form, meaning the phone.

The basic noun is:

• en telefon = a phone

Since telefon is an en-word (a common-gender noun), the definite ending is -en:

• en telefon = a phone
• telefonen = the phone

So the sentence uses two definite nouns:

• simkortet = the SIM card
• telefonen = the phone

Because Swedish usually puts the definite article at the end of the noun instead of using a separate word before it.

So:

• simkortet = the SIM card
• telefonen = the phone

This is very common in Swedish. English uses a separate word, but Swedish often uses a suffix.

A separate definite word can appear in other patterns, such as:

• den nya telefonen = the new phone

But in your sentence, no separate word is needed.

I means in or inside.

That fits here because the SIM card is inside the phone.

• i telefonen = in the phone

You would not normally use på here, because på usually means on or on top of in this kind of situation.

So:

• i telefonen = correct
• på telefonen = would sound wrong for a SIM card

The sentence follows normal Swedish statement word order:

• Simkortet = subject
• sitter = verb
• i telefonen = place expression

So the pattern is:

• subject + verb + adverbial/place

This is a very standard Swedish main clause.

Yes. Swedish is a V2 language, which means the finite verb usually stays in the second position in main clauses.

So you can also say:

• I telefonen sitter simkortet.

This still means the same thing, but now the sentence puts more focus on where the SIM card is.

Notice that sitter is still in second position.

You usually make a yes/no question by putting the verb first:

• Sitter simkortet i telefonen?

That is the normal Swedish pattern for this kind of question.

So:

• statement: Simkortet sitter i telefonen.
• question: Sitter simkortet i telefonen?

You add inte after the finite verb:

• Simkortet sitter inte i telefonen.

In a normal Swedish main clause, inte usually comes after the verb.

So the pattern is:

• subject + verb + inte + rest

Yes.

• simkort is an ett-word
• telefon is an en-word

That is why their definite forms look different:

• ett simkort → simkortet
• en telefon → telefonen

This is an important thing to learn in Swedish, because noun gender affects articles and endings.