Se eu esquecer o telefone em casa, vou voltar para pegar.

Because Portuguese normally uses the future subjunctive after se when talking about a real possibility in the future.

So:

• Se eu esquecer... = If I forget...
• Se eu esqueço... would sound unnatural in this meaning

This is a very common pattern:

• Se eu tiver tempo, eu vou. = If I have time, I’ll go.
• Se chover, ficamos em casa. = If it rains, we stay home.

In this sentence, esquecer is the future subjunctive form.

That is normal. For many verbs, some forms of the future subjunctive are identical to the infinitive.

With esquecer:

• infinitive: esquecer
• future subjunctive, eu: esquecer
• future subjunctive, você/ele/ela: esquecer

So even though it looks like the infinitive, in Se eu esquecer, it is functioning as the future subjunctive.

Yes, Portuguese often omits subject pronouns, but here eu is very helpful.

The form esquecer could refer to:

• eu esquecer
• você esquecer
• ele/ela esquecer

So saying eu makes the subject clear.

You could also say:

• Se esquecer o telefone em casa, vou voltar para pegar.

But this is less clear and sounds more natural only when the context already makes it obvious that the speaker means I.

Both are correct, but vou voltar is much more common in everyday Brazilian Portuguese.

• vou voltar = going to go back / will go back
• voltarei = I will go back

In spoken Brazilian Portuguese, ir + infinitive is usually the most natural way to talk about the future.

So:

• Se eu esquecer o telefone em casa, vou voltar para pegar. = very natural speech
• Se eu esquecer o telefone em casa, voltarei para pegá-lo. = correct, but more formal or written

Here voltar means to go back or to return.

So vou voltar means:

• I’ll go back
• I’ll return

In this sentence, the idea is going back to the place where the phone was left.

Para + infinitive often means in order to or to do something.

So:

• voltar para pegar = go back to get/pick up it

It expresses purpose.

Other examples:

• Saí cedo para trabalhar. = I left early to work.
• Abri a janela para entrar ar. = I opened the window to let air in.

In speech, para often becomes pra:

• vou voltar pra pegar

That is very common in Brazil.

Because Portuguese, like English, can omit an object when it is already obvious from context.

Here:

• o telefone is mentioned first
• then pegar is understood as pegar o telefone

So vou voltar para pegar means I’ll go back to get it.

If you want to make it explicit, you could say:

• vou voltar para pegá-lo

That is more formal and more typical in writing.

In everyday spoken Brazilian Portuguese, many people would also say:

• vou voltar para pegar ele

This is common in speech, although more traditional grammar prefers pegá-lo.

When object pronouns like lo, la, los, las are attached to an infinitive ending in -r, the -r drops and an accent is added.

So:

• pegar + lo → pegá-lo
• fazer + la → fazê-la
• ver + o does not work the same way because ver uses different pronoun patterns depending on structure

This is a standard written pattern in Portuguese.

No. Pegar is a very flexible verb in Brazilian Portuguese.

In this sentence, it means to get, to pick up, or to retrieve.

So voltar para pegar means:

• go back to get it
• go back to pick it up

Depending on context, pegar can also mean things like:

• to catch a bus: pegar o ônibus
• to catch a disease: pegar gripe
• to grab/take something: pegar a chave

Because Portuguese often uses the definite article when possession is obvious from context.

So o telefone here naturally implies my phone, since the speaker is talking about forgetting it at home.

Both are possible:

• Se eu esquecer o telefone em casa... = natural, possession understood
• Se eu esquecer meu telefone em casa... = also correct, a bit more explicit

Using meu can add emphasis or clarity, but it is not necessary.

Em casa means at home.

This is the normal expression when talking about being at one’s own home or home in a general sense.

• Estou em casa. = I’m at home.
• Esqueci o telefone em casa. = I forgot the phone at home.

Na casa means in/at the house, usually a specific house, often someone else’s or one already identified.

For example:

• Estou na casa da minha amiga. = I’m at my friend’s house.

So in your sentence, em casa is the natural choice.

It is standard and helpful because the sentence has two parts:

• Se eu esquecer o telefone em casa = the condition
• vou voltar para pegar = the result

So the comma separates the if-clause from the main clause.

You will usually see it written this way:

• Se eu esquecer o telefone em casa, vou voltar para pegar.

In very informal writing, people may leave it out, but the comma is the correct standard punctuation.

Yes, absolutely. In Brazilian Portuguese, celular is often more common than telefone when people mean a mobile phone.

So:

• telefone = phone
• celular = cell phone / mobile phone

If the meaning is specifically a mobile phone, many Brazilians would naturally say:

• Se eu esquecer o celular em casa, vou voltar para pegar.

That may sound even more everyday and natural in Brazil today.

Yes. In spoken Brazilian Portuguese, pra is extremely common and natural.

So these are both correct:

• vou voltar para pegar
• vou voltar pra pegar

The difference is mostly register:

• para = neutral, standard, good in writing
• pra = informal, very common in speech

A Brazilian speaker would very often say:

• Se eu esquecer o telefone em casa, vou voltar pra pegar.