jaekis jumeonie hyudaeponeul neoheo dumyeon soni pyeonhaeyo.

넣어 두다 is a very common grammar pattern in Korean.

• 넣다 = to put in
• 넣어 두다 = to put in and leave it there / put it in beforehand

So:

• 휴대폰을 넣으면 = if you put the phone in
• 휴대폰을 넣어 두면 = if you put the phone in and keep it there

In this sentence, 넣어 두면 gives the idea of doing it in advance so the result continues. It feels natural because the phone stays in the jacket pocket, which then makes your hands free.

-면 means if or when.

Here:

• 휴대폰을 넣어 두면 = if/when you put your phone in your jacket pocket and leave it there
• 손이 편해요 = your hands are comfortable / free / it’s easier on your hands

So -면 connects a condition to a result.

A simple way to think about it:

• A-면 B = If A happens, B happens

Because 에 marks the place where something is put.

• 주머니에 넣다 = to put something into a pocket
• 가방에 넣다 = to put something into a bag

So in this sentence:

• 재킷 주머니에 = in the jacket pocket
• 휴대폰을 = the phone (object)
• 넣어 두면 = if you put it in and leave it there

The pocket is the destination/location, so 에 is correct.

-을 / -를 is the object marker.

Here, 휴대폰을 tells you that 휴대폰 is the thing being put into the pocket.

So the structure is:

• 재킷 주머니에 = into the jacket pocket
• 휴대폰을 = the cell phone
• 넣어 두면 = if you put it in and leave it there

A literal breakdown is:

• Put the cellphone into the jacket pocket and leave it there

Yes, this is a very natural Korean expression, but it does not map neatly into English word-for-word.

손이 편하다 often means:

• your hands are free
• it’s convenient for your hands
• you don’t have to keep holding something
• it feels easier physically

So in this sentence, 손이 편해요 means something like:

• your hands are free
• it’s easier because you don’t have to hold your phone
• your hands are more comfortable

Korean often uses body-part subjects in ways that sound unusual in English.

Because 편하다 describes a state, and the thing in that state is marked with 이/가.

So:

• 손이 편해요 = the hands are comfortable / your hands feel free

Compare:

• 손을 씻어요 = wash your hands
  Here 손 is the object, so it takes -을.
• 손이 아파요 = my hand hurts
  Here 손 is the subject of the condition, so it takes -이.
• 손이 편해요 = my hands are comfortable/free
  Same idea.

Yes. 재킷 is a loanword from English jacket.

A few notes:

• It is pronounced in a Korean way: roughly jae-kit
• In everyday life, some people also write or say 자켓, though 재킷 is the standard spelling
• 재킷 주머니 means jacket pocket

So the first part of the sentence is literally:

• 재킷 주머니에 = in the jacket pocket

Korean often leaves out possessives like my, your, or his/her when they are obvious from context.

So:

• 손이 편해요 literally = the hands are comfortable
• natural English = your hands are free / it’s easier on your hands

Because the whole sentence is giving general advice, Korean does not need to say your hands explicitly.

This is very common with body parts:

• 머리가 아파요 = I have a headache / my head hurts
• 눈이 아파요 = my eyes hurt
• 손이 편해요 = my/your hands feel free or comfortable

Yes. In real usage, you will often see both:

• 넣어 두면
• 넣어두면

The spaced version can make the grammar easier to see for learners:

• 넣어 두다 = put in and leave there

The attached version is also very common in everyday writing. Both are understood.

편해요 is the 해요-style polite form.

• dictionary form: 편하다
• polite present: 편해요

This style is polite and very common in daily conversation. It is less formal than 편합니다, but still respectful.

So this sentence sounds like natural everyday polite Korean.

Yes. Depending on context, natural English translations could include:

• If you put your phone in your jacket pocket, your hands are free.
• If you keep your phone in your jacket pocket, it’s easier on your hands.
• If you put your phone in your jacket pocket, you don’t have to hold it, so it’s more convenient.
• If you keep your phone in your jacket pocket, your hands are freer.

This is a good example of a sentence whose Korean meaning is simple, but the most natural English translation depends on context.