Cha của Lan gọi điện nói là ông ấy sẽ về muộn vì xe buýt đến trễ.

Của is the common Vietnamese word for possession, similar to of or 's in English.

So:

• Cha của Lan = Lan's father
• literally: father of Lan

Vietnamese often uses this pattern:

• mẹ của tôi = my mother
• nhà của anh ấy = his house

In everyday speech, people may also say cha Lan in some contexts, but cha của Lan is very clear and standard for learners.

Vietnamese has several words for father, and the choice depends on region, style, and family habit.

Common options include:

• cha – somewhat formal, literary, or common in some regions/religious contexts
• ba – very common in the South
• bố – very common in the North
• baba / tía / thầy – more regional or old-fashioned in some places

So cha của Lan means the same basic thing as bố của Lan or ba của Lan: Lan's father. The difference is mostly tone and regional preference, not meaning.

Gọi điện means to call on the phone or to phone someone.

Breakdown:

• gọi = call
• điện = electricity/electronic communication, and in this phrase it refers to a phone call

So:

• Cha của Lan gọi điện = Lan's father called / phoned

You may also hear:

• gọi điện thoại = call by phone

That version is a little fuller, but gọi điện is very common and natural.

In this sentence, nói là means said that.

So:

• gọi điện nói là ông ấy sẽ về muộn... = called and said that he would come home late...

Here, là works a bit like the English connector that introducing reported speech or information.

Examples:

• Anh ấy nói là anh ấy bận. = He said that he was busy.
• Cô ấy bảo là mai đến. = She said to come tomorrow.

In casual speech, là is sometimes omitted:

• Cha của Lan gọi điện nói ông ấy sẽ về muộn...

That is also natural.

Ông ấy is a third-person pronoun referring back to Lan's father.

Here:

• ông = a respectful pronoun for an older man
• ấy = that/he

So ông ấy = he (referring to an older man)

Vietnamese often uses pronouns based on age, status, and relationship, rather than a single neutral word like English he.

This avoids repeating cha của Lan and sounds natural.

Yes, often it could be omitted if the meaning is already clear from context.

For example:

• Cha của Lan gọi điện nói là sẽ về muộn vì xe buýt đến trễ.

This is still understandable and natural.

Vietnamese frequently drops subjects when they are obvious. But including ông ấy makes the reference extra clear, especially in a longer sentence.

Sẽ is a future marker. It often means will or going to.

So:

• ông ấy sẽ về muộn = he will come home late / he’ll be home late

Without sẽ, the sentence could still make sense in the right context, because Vietnamese often relies on context rather than tense endings. But sẽ clearly marks the event as future from the time of the phone call.

Compare:

• ông ấy về muộn = he comes home late / he is coming home late / he came home late, depending on context
• ông ấy sẽ về muộn = he will come home late

Về means to return / to come back / to go home, depending on context.

So:

• sẽ về muộn = will come home late or will return late

If you say only:

• ông ấy sẽ muộn

that sounds incomplete or unnatural in many situations, because muộn usually describes being late for something or happening late. The verb về tells us what action is late: his returning home.

Both muộn and trễ can mean late, and in many contexts they overlap.

In this sentence:

• về muộn = come home late
• đến trễ = arrive late

Using both in one sentence is completely fine.

A few notes:

• muộn is very common across Vietnam
• trễ is also common, especially in Southern speech
• In some contexts, one may sound a bit more natural than the other, but both are widely understood

You could also say:

• ông ấy sẽ về trễ
• xe buýt đến muộn

Those are also understandable.

Yes. Here đến means arrive.

So:

• xe buýt đến trễ = the bus arrived late or the bus is late arriving

This explains the reason for the father's late return.

Notice that đến is used for arrival in many contexts:

• Tôi đến trường lúc 7 giờ. = I arrive at school at 7.
• Khi nào xe đến? = When does the bus/train/car arrive?

Vì means because.

So:

• vì xe buýt đến trễ = because the bus arrived late

Yes, you could also use bởi vì:

• ...bởi vì xe buýt đến trễ

That has the same meaning, but vì is shorter and very common in everyday Vietnamese.

You may also see:

• do = because of / due to
• tại = because of, often in speech

Examples:

• muộn vì kẹt xe = late because of traffic
• muộn do thời tiết xấu = late due to bad weather

Grammatically, ông ấy could refer to another older man if the wider context introduced one. But in this sentence by itself, the natural interpretation is that ông ấy refers to Lan's father.

That is because:

1. Lan's father is the main person mentioned first.
2. He is the one who called.
3. It makes logical sense that he is the one who will be home late.

So in normal reading, there is little real confusion.

A fairly literal breakdown is:

• Cha của Lan = Lan's father
• gọi điện = called / phoned
• nói là = said that
• ông ấy = he
• sẽ về muộn = will return home late
• vì = because
• xe buýt = bus
• đến trễ = arrived late / came late

So a very literal English version would be:

Lan's father phoned, saying that he would return home late because the bus arrived late.

This kind of breakdown is useful because Vietnamese does not change verb forms for tense the way English does. Instead, meaning comes from words like sẽ and from context.