Learn Hardcore Turkish: Telefonu sessiz moda alınca izleyiciler daha iyi odaklanıyor. - When you put the phone on silent mode, the audience focuses better.

Because almak is a transitive verb and the phone is a specific/direct object here. The accusative -u marks specificity: telefonu sessiz moda almak = “to put the phone into silent mode.” If you drop -u, you either make the object non-specific (odd here) or risk parsing telefon as a subject. If you want to avoid stating who does the action, you can use the passive: Telefon sessiz moda alınınca… (“When the phone is put into silent mode…”).

Who is the subject of alınca? It isn’t written.

With -(y)ınca clauses, the understood subject is usually controlled by the main clause subject. So here it’s the same as izleyiciler: “When the viewers put the phone on silent mode, the viewers focus better.” If you don’t want to imply that the viewers themselves do the action, use a passive or state a different subject:

Passive: Telefon sessiz moda alınınca…
Different explicit subject: Siz telefonu sessiz moda alınca izleyiciler…

Why use -(y)ınca here? How would -dığında or -ken change the meaning?

alınca = “when/once (someone) puts it,” event-focused and common in speech.
alındığında (passive + -dığında) = “when it is put,” more formal/neutral, often used when the agent is irrelevant.
alırken = “while putting,” simultaneous/ongoing action, not a boundary event.
For a state rather than an action, Turkish often uses olunca: Telefon sessiz modda olunca… (“When the phone is in silent mode…”).

What’s the difference between alınca and alınınca?

alınca = active: “when (someone) puts [it].”
alınınca = passive: “when [it] is put.”
Use alınca if you want the subject of the main clause to also be the doer; use alınınca if you want to avoid mentioning the agent.

Why is it moda (dative -a), not modda (locative -da)?

Dative -a/-e marks movement into a state/place: sessiz mod-a almak = “put into silent mode.” Locative -da/-de marks being in a state: sessiz mod-da olunca = “when it is in silent mode.”

Is sessize almak more idiomatic than sessiz moda almak?

Yes, telefonu sessize almak (“to silence the phone”) is very common and slightly shorter. Sessiz moda almak is also correct and explicit (“put into silent mode”). You’ll also hear:

Subject switches itself: Telefon sessiz moda geçince…
Avoid forms like sessize getirmek; the idiom is sessize almak.

Why does the main verb use odaklanıyor (progressive) instead of odaklanır (aorist)?

odaklanır states a general truth/habit: “viewers (in general) focus better.”
odaklanıyor in spoken Turkish often reports an observed/typical tendency (“we see that they focus better when this happens”). Both are acceptable; choose aorist for timeless generalization and -yor for a current/observational generalization.

Should it be odaklanıyorlar since izleyiciler is plural?

The 3rd-person plural ending on the verb (-lar) is optional.

izleyiciler … odaklanıyor is fine and common.
izleyiciler … odaklanıyorlar explicitly marks plural on the verb and is often preferred with human subjects, especially in careful style. No change in meaning.

Do we need a comma after the -(y)ınca clause?

It’s optional but recommended for readability: Telefonu sessiz moda alınca, izleyiciler… Many writers omit it in short sentences, but adding the comma is good practice.

Could/should we mark whose phone it is? Would telefonlarını be better?

You can. Telefonu can be understood generically as “the phone,” but if you want to be explicit that it’s their own phones, say:

İzleyiciler telefonlarını sessize alınca daha iyi odaklanıyor(lar).
That’s very natural in many contexts (e.g., instructions to an audience).

Is the placement of daha iyi correct? Can it move?

Yes. Adverbs usually precede the verb phrase. The most neutral spots are before the verb or just after the subject:

İzleyiciler daha iyi odaklanıyor(lar).
You can also put it near the end for emphasis: … odaklanıyor(lar) daha iyi, but that sounds marked and is less common.

Can I move the -(y)ınca clause elsewhere?

Yes; Turkish word order is flexible for adverbials. All are possible, with slight changes in emphasis:

Telefonu sessiz moda alınca, izleyiciler daha iyi odaklanıyor. (neutral)
İzleyiciler, telefonu sessiz moda alınca, daha iyi odaklanıyor. (focus on viewers)
İzleyiciler daha iyi odaklanıyor, telefonu sessiz moda alınca. (end-focus on the condition)

What does odaklanmak require? Do I need a preposition for “focus on”?

Odaklanmak is intransitive and takes the dative for its target: Neye odaklanmak? (“focus on what?”). Here, the target is implicit. Example: Derse/ekrana odaklanıyorlar (“They focus on the lesson/screen”).

Can you break down the morphology of the sentence?

Telefon-u = telefon + Accusative (-u) “the phone (object)”
sessiz mod-a = “silent mode” + Dative (-a) “into silent mode”
al-ınca = al- “take/put” + -(y)ınca “when/once”
izleyici-ler = izleyici “viewer” + plural (-ler)
daha iyi = “more good” → “better”
odaklan-ıyor (-lar) = odaklan- “focus (derivational -lAn)” + progressive (-yor) + optional 3rd plural (-lar)