Sy skakel haar suster, omdat sy haar stem wil hoor.

Here skakel means call / phone / contact.

So Sy skakel haar suster = She calls her sister.

A useful note: in everyday Afrikaans, many speakers very often use bel for phone/call:

• Sy bel haar suster.

Skakel is still correct, but it can sound a bit more formal or broader, since it can also mean connect or switch in other contexts.

Both instances of sy mean she.

• Sy skakel haar suster = She calls her sister
• omdat sy haar stem wil hoor = because she wants to hear her voice

Afrikaans often repeats the pronoun where English would also repeat it. So there is nothing unusual here.

Also remember that sy is the subject pronoun form:

• Sy praat. = She speaks.

Because haar is the form used for her before a noun.

So:

• sy = she
• haar = her

In this sentence, haar is possessive both times:

• haar suster = her sister
• haar stem = her voice

Compare:

• Sy is hier. = She is here.
• Ek sien haar. = I see her.
• Haar boek is op die tafel. = Her book is on the table.

So an English speaker can think of it like this:

• sy = subject form (she)
• haar = object/possessive form (her)

Because omdat introduces a subordinate clause, and in Afrikaans subordinate clauses the verbal part goes to the end.

Main clause:

• Sy wil haar stem hoor.
• literally: She wants her voice hear

After omdat:

• ..., omdat sy haar stem wil hoor.

So the pattern is:

• omdat + subject + other information + verbs at the end

This is one of the most important word-order patterns in Afrikaans.

More examples:

• Ek bly tuis, omdat ek moeg is.
• Hy kom nie, omdat hy moet werk.

Because wil is a modal verb, and modal verbs in Afrikaans are followed directly by the infinitive.

So:

• sy wil hoor = she wants to hear
• not sy wil om hoor

This is the same pattern you get with other modal verbs:

• Ek kan swem. = I can swim.
• Jy moet gaan. = You must go.

Afrikaans does use om te in other structures, but not after a modal like wil, kan, moet, mag.

Yes, it can be ambiguous.

Sy skakel haar suster, omdat sy haar stem wil hoor could mean:

1. She calls her sister because she wants to hear her sister’s voice, or
2. She calls her sister because she wants to hear her own voice

In real context, people would usually understand the intended meaning from the situation. But grammatically, it is not completely clear.

If you want to make it clearer, you can say:

• ... omdat sy haar suster se stem wil hoor. = ... because she wants to hear her sister’s voice
• ... omdat sy haar eie stem wil hoor. = ... because she wants to hear her own voice

That little word eie is very useful for showing her own.

Yes, very often you can.

With want, the meaning is still because, but the word order changes.

With omdat:

• Sy skakel haar suster, omdat sy haar stem wil hoor.

With want:

• Sy skakel haar suster, want sy wil haar stem hoor.

Notice the difference:

• after omdat, the verb goes to the end of the clause
• after want, the clause keeps normal main-clause word order

A simple way to remember it:

• omdat = subordinate clause
• want = coordinating clause

Because in Afrikaans, a subordinate clause introduced by a conjunction like omdat is normally separated from the main clause with a comma.

So:

• Sy skakel haar suster, omdat sy haar stem wil hoor.

You will see the same with other conjunctions too:

• Ek gaan huis toe, as dit reën.
• Hy sê, dat hy later kom.

So the comma here is normal Afrikaans punctuation.

Because once you use a possessive word like haar (her), you do not also use die.

So:

• haar suster = her sister
• not die haar suster

And:

• haar stem = her voice
• not die haar stem

This works just like English:

• her sister, not the her sister

So haar already does the job of specifying the noun.