jihacheoreseoneun tonghwaga jal an dwaeyo.

-에서는 is -에서 + 는.

• 지하철에서 = in/on the subway
• 지하철에서는 = as for in/on the subway, or at least on the subway

The extra 는 adds a topic/contrast feeling. It can suggest something like:

• On the subway, phone calls don’t work well
  (maybe in other places they do)

So the sentence is not just stating location; it is highlighting the subway as the setting being talked about.

Also, English says on the subway, but Korean uses 에서 for the place where something happens. So even though English uses on, Korean uses a location particle here.

통화 means a phone call or talking on the phone.

In this sentence, it refers to the act of having a phone conversation, not just the device itself.

Some useful related words:

• 전화 = telephone / phone call
• 통화 = phone conversation, being connected and talking
• 통화하다 = to talk on the phone

So 통화가 잘 안 돼요 is more like phone calls don’t go through well or it’s hard to talk on the phone, not just there is no phone.

Because the verb phrase is 잘 안 되다, not 하다.

With 되다, the thing that works / is possible / goes through often takes -가. Here, 통화 is the thing that is or is not working well:

• 통화가 잘 돼요 = phone calls work well
• 통화가 잘 안 돼요 = phone calls don’t work well

If you said 통화를, that would usually go with a verb like 하다:

• 통화를 해요 = I make a phone call / I talk on the phone

So:

• 통화가 잘 안 돼요 = the call itself doesn’t go through well
• 통화를 잘 안 해요 = I don’t make phone calls much / I don’t talk on the phone much

Those are different meanings.

Literally, it is something like doesn’t become well or doesn’t work well.

Breakdown:

• 잘 = well
• 안 = not
• 돼요 = becomes / works / is possible

In natural English, 잘 안 되다 often means:

• doesn’t work well
• is difficult
• doesn’t go through
• is not easy

So 통화가 잘 안 돼요 is a very natural Korean way to say that phone calls are hard to make or do not connect well.

Not in this sentence.

안 되다 can mean different things depending on context:

• That won’t work / it’s not possible
• You mustn’t / that’s not allowed

Here, because the sentence says 통화가 잘 안 돼요, it means phone calls don’t work well or it’s hard to get a good connection.

The 잘 is important. It strongly suggests a problem with how well something works, not a rule or prohibition.

Compare:

• 여기서 통화하면 안 돼요. = You must not talk on the phone here.
• 여기서 통화가 잘 안 돼요. = Phone calls don’t work well here.

Yes, you could, but the nuance is a little different.

• 통화가 잘 안 돼요 focuses on the situation or connection.
  It sounds like the environment is the problem: bad signal, noise, underground location, etc.

• 통화를 잘 못 해요 focuses more on the person’s ability to do the action.
  It can mean I can’t talk on the phone well there.

In everyday speech, both can be understood similarly, but the original sentence is especially natural when the problem is external, like reception.

You could also say:

• 지하철에서는 통화하기가 어려워요. = It’s difficult to talk on the phone on the subway.
• 지하철에서는 통화할 수 없어요. = You can’t talk on the phone on the subway.

These are understandable, but 통화가 잘 안 돼요 sounds very natural for the call doesn’t go through well.

Because 돼요 comes from 되어요, which contracts to 돼요.

So:

• 되어요 → 돼요
• not 되요

This is a very common spelling point in Korean.

For the verb 되다:

• 돼요 = correct
• 되요 = incorrect standard spelling

A quick check learners sometimes use: If you can expand it to 되어, then 돼 is right.

• 안 돼요 → 안 되어요
  So 돼요 is correct.

It is in the standard polite style, often called 해요체.

That makes it appropriate for many everyday situations:

• talking to strangers
• talking to coworkers in casual-polite settings
• talking to service staff
• general conversation

Other levels:

• 통화가 잘 안 됩니다. = more formal
• 통화가 잘 안 돼. = casual/informal

So the sentence as written is polite and very commonly used in daily speech.