Learn Hardcore Arabic (Levantine): كل الكتب بالخزانة.

كل is often pronounced kell
الكتب is often pronounced il-ktob in Levantine
بالخزانة is bil-khizāne
The kh sound in khizāne is the throaty sound you hear in Scottish loch or German Bach

Depending on the country or speaker, you may hear small differences, but this is a very natural Levantine reading.

Why is there no word for are in this sentence?

Because in Arabic, especially in the present tense, you usually do not use a verb like is/are in simple equational sentences.

So English says:

All the books are in the cabinet.

But Arabic simply says:

All the books in the cabinet.

That is completely normal. The idea of are is understood automatically.

If you wanted past or future, then Arabic would use other forms, but in a present-time statement like this, no separate word for are is needed.

What does كل mean here, and why is it singular-looking?

كل means all or every, depending on context.

In this sentence, means .