När jag trycker på porttelefonen säger hon att portkoden har ändrats.

Because the sentence begins with När jag trycker på porttelefonen, which is a subordinate clause.

In Swedish main clauses, the finite verb normally has to come in second position. So after the whole När... clause, the verb comes first:

• När jag trycker på porttelefonen säger hon...

This is a very common Swedish word-order pattern. Compare:

• Hon säger att... = She says that...
• När jag trycker på porttelefonen säger hon att... = When I press the intercom, she says that...

So the inversion happens because something else came first.

När means when.

It introduces a subordinate clause:

• När jag trycker på porttelefonen = When I press the intercom

In this sentence, it can also feel a bit like whenever, because the present tense suggests a repeated or typical situation, not necessarily one single event.

Because trycka på is the normal expression for pressing/pushing something, especially a button or device.

• trycka = press, push, print, squeeze, depending on context
• trycka på = press on / push / press a button

So:

• trycka på porttelefonen = press the intercom / press the entry phone button

The på is part of the expression here, so it should not be translated too literally every time.

Porttelefonen is a compound noun:

• port = entrance gate, building entrance, outer door
• telefon = telephone

Together, porttelefon means entry phone, door intercom, or building intercom.

The ending -en makes it definite:

• en porttelefon = an intercom
• porttelefonen = the intercom

Because Swedish usually puts the definite article at the end of the noun.

So:

• porttelefon = intercom
• porttelefonen = the intercom

and

• portkod = door code / entry code
• portkoden = the door code

This is one of the big differences from English. Instead of a separate word like the, Swedish often uses a suffix such as -en or -et.

Att means that here.

It introduces the clause that tells us what she says:

• säger hon att portkoden har ändrats
• she says that the door code has been changed

In English, that is often optional:

• She says that the door code has been changed.
• She says the door code has been changed.

In Swedish, att is very common in this kind of sentence.

Because after att, Swedish uses subordinate clause word order.

That means the subject usually comes before the finite verb:

• att portkoden har ändrats

not

• att har portkoden ändrats

So there is a contrast:

• Main clause: säger hon
• Subordinate clause: att portkoden har ändrats

This difference between main-clause word order and subordinate-clause word order is very important in Swedish.

Har ändrats means has been changed or sometimes has changed, depending on context.

Here it is best understood as:

• portkoden har ändrats = the door code has been changed

This is the present perfect:

• har = has
• ändrats = changed

So it describes something that happened earlier but is still relevant now.

The -s marks the passive voice.

The basic verb is:

• ändra = to change something

Passive forms are often made with -s in Swedish:

• ändras = be changed / get changed
• har ändrats = has been changed

So instead of saying who changed the code, the sentence focuses on the result: the code is different now.

Another possible passive form would be:

• har blivit ändrad

But har ändrats is very natural and common.

Because Swedish often uses the present tense for a general, habitual, or repeated situation.

So:

• När jag trycker på porttelefonen säger hon...

means something like:

• When/Whenever I press the intercom, she says...

It sounds like this is what normally happens.

If you wanted to talk about one specific event in the past, you would use past tense instead:

• När jag tryckte på porttelefonen sa hon att portkoden hade ändrats.
• When I pressed the intercom, she said that the door code had been changed.

Usually, no comma is needed here in modern Swedish.

So this is normal:

• När jag trycker på porttelefonen säger hon att portkoden har ändrats.

Swedish generally uses commas less often than English. A comma after an introductory subordinate clause is sometimes possible for clarity or style, but it is often omitted.