Я специально выключил телефон, чтобы спокойно поработать.

Because выключил is perfective. It presents the action as a completed whole: I turned off the phone.

In this sentence, the speaker means they did one complete action on purpose in order to achieve a goal. That makes the perfective natural.

• выключил = turned off, completed the action
• выключал = was turning off / used to turn off / turned off repeatedly, depending on context

Here, the idea is:

• first, the speaker turned off the phone,
• then, as a result, they could work peacefully.

So perfective fits better.

выключил is the past tense masculine singular form.

Russian past tense agrees with the subject in gender and number:

• я выключил — if the speaker is male
• я выключила — if the speaker is female
• мы выключили — we turned off
• они выключили — they turned off

So this sentence suggests that the speaker is male. If a woman said it, it would be:

Я специально выключила телефон, чтобы спокойно поработать.

Because Russian often does not repeat the subject when it is already clear.

In English, you might say:

• I turned off my phone so that I could work peacefully.

In Russian, the subject of поработать is understood automatically from the context:

• Я ... чтобы спокойно поработать
• literally: I ... in order to work peacefully

Russian does this very naturally. If the subject is the same person, it usually does not need to be repeated.

специально means something like:

• on purpose
• deliberately
• specifically for this reason

So Я специально выключил телефон means:

• I deliberately turned off the phone
• I turned off the phone on purpose

It emphasizes that this was intentional, not accidental or automatic.

A useful contrast:

• специально = deliberately, intentionally
• случайно = accidentally

For example:

• Я специально это сделал. — I did it on purpose.
• Я случайно это сделал. — I did it by accident.

Yes, Russian word order is fairly flexible, but the usual order here is natural and neutral:

Я специально выключил телефон...

This puts the emphasis on the fact that the action was intentional.

Other word orders are possible, but they may change emphasis slightly:

• Я выключил телефон специально...
  This can sound like you are emphasizing that it was deliberate, perhaps in contrast to another possibility.

• Специально я выключил телефон...
  This is possible, but more marked and less neutral in ordinary speech.

So the given order is the most normal everyday way to say it.

Because телефон is the direct object of выключил, and for an inanimate masculine noun, the accusative singular is the same as the nominative singular.

So:

• nominative: телефон
• accusative: телефон

That is why you see:

• выключил телефон — turned off the phone

Compare with a feminine noun:

• выключил лампу — turned off the lamp

And with an animate masculine noun, the accusative would often match the genitive instead:

• вижу брата — I see my brother

But телефон is inanimate, so телефон stays the same.

чтобы means so that, in order to, or for the purpose of.

It introduces a purpose clause:

• Я специально выключил телефон, чтобы спокойно поработать.
• I deliberately turned off the phone so that I could work peacefully.

This word is very common when talking about goals or purpose.

Examples:

• Я пришёл рано, чтобы помочь. — I came early to help.
• Он открыл окно, чтобы проветрить комнату. — He opened the window to air out the room.

So in your sentence, чтобы connects the main action with its purpose.

This is an important aspect question.

поработать is a perfective verb formed from работать. It often means:

• to work for a while
• to get some work done
• to do a bit of work

So спокойно поработать is not just to work peacefully, but often more specifically:

• to work peacefully for some time
• to get some peaceful work done

Compare:

• работать — to work, be working, work in general
• поработать — to work for a while / do some work as a completed stretch

In purpose clauses after чтобы, both aspects are possible, but they give different shades of meaning.
Here, поработать sounds very natural because the speaker has a clear goal: to have an uninterrupted period of work.

In this verb, по- often adds the idea of doing something for a limited time or as a bounded, complete stretch.

So:

• работать — to work
• поработать — to work for a bit / to spend some time working / to get some work done

This use of по- is very common with verbs:

• посидеть — sit for a while
• поспать — sleep for a while
• погулять — take a walk / walk for a while
• почитать — read for a while

So спокойно поработать suggests a finite, successful period of peaceful work.

Literally, спокойно can mean:

• calmly
• peacefully
• quietly
• without disturbance

In this sentence, the most natural sense is:

• peacefully
• without interruptions
• in peace and quiet

So it is less about the speaker’s inner emotional state and more about the working conditions.
The idea is something like:

• to work without being bothered
• to work in peace

That is why turning off the phone makes sense as the reason.

Because чтобы introduces a subordinate clause, and in Russian such clauses are normally separated by a comma.

So the structure is:

• main clause: Я специально выключил телефон
• subordinate purpose clause: чтобы спокойно поработать

Hence:

Я специально выключил телефон, чтобы спокойно поработать.

This comma is required in standard Russian punctuation.

Yes. In Russian, possessive words like мой / моя / моё are often omitted when possession is obvious from context.

So выключил телефон often naturally means:

• turned off the phone
• and in context, very often turned off my phone

If needed, Russian can say:

• Я специально выключил свой телефон...
• Я специально выключил мой телефон... (less common in this kind of context)

Usually свой is preferred when the object belongs to the subject:

• Я выключил свой телефон.

But in everyday Russian, leaving it out is very common when the meaning is obvious.

Yes, you can say:

Я специально выключил телефон для того, чтобы спокойно поработать.

This also means in order to work peacefully.

But there is a difference in style:

• чтобы = shorter, more natural, more conversational
• для того, чтобы = more explicit, more formal, sometimes more emphatic

In ordinary speech, чтобы is usually the best choice here.