Zapisuję dane w telefonie.

Zapisuję is the 1st person singular present tense form of the verb zapisywać.

So:

• zapisywać = to be writing down / to be recording / to be saving
• zapisuję = I am writing down / I write down / I am saving

In this sentence, it matches I because the -ę ending marks 1st person singular.

A quick mini-paradigm:

• ja zapisuję = I write down / save
• ty zapisujesz = you write down / save
• on/ona zapisuje = he/she writes down / saves

Polish often leaves out the subject pronoun ja, because the verb ending already shows who is doing the action.

Yes. Polish present tense often covers both:

• I write down
• I am writing down

So zapisuję dane can mean either:

• I write down/save data
• I am writing down/saving data

Polish usually does not make the same continuous vs. simple distinction that English does here. Context tells you which English translation sounds best.

This is a very common Polish question because it involves aspect.

• zapisywać = imperfective
• zapisać = perfective

In simple terms:

• imperfective focuses on the process, repetition, or ongoing action
• perfective focuses on the action as completed

So:

• Zapisuję dane = I am saving / I save data
• Zapiszę dane = I will save the data
• Zapisałem dane = I saved the data / I have saved the data

A very important point:
The perfective verb zapisać does not normally have a true present-tense meaning. Its present forms usually refer to the future.

Dane is normally used as a plural noun meaning data.

So in Polish:

• dane = data
• it behaves grammatically as plural

That is why you do not say dana here.

Examples:

• Zapisuję dane. = I am saving data.
• Te dane są ważne. = This data is important.

In everyday Polish, dane is the normal word for data, especially in technical, digital, or administrative contexts.

Here dane is in the accusative case, because it is the direct object of zapisuję.

You are saving what?
→ dane

For this noun, the accusative form looks the same as the nominative form:

• nominative: dane
• accusative: dane

So even though the case is accusative, the word does not visibly change here.

Because the preposition w meaning in requires the locative case when it expresses location.

So:

• telefon = phone
• w telefonie = in the phone

The ending changes because of the locative:

• telefon → telefonie

This is very common in Polish:

• w domu = in the house
• w sklepie = in the shop
• w komputerze = in the computer
• w telefonie = in the phone

Yes, literally it means in the phone, and that is normal Polish.

English often says:

• on my phone

But Polish commonly says:

• w telefonie = in the phone
• sometimes also na telefonie, but that usually means something else depending on context

For storing or having data inside the device, w telefonie is very natural.

So even if English prefers on my phone, Polish often uses the equivalent of in my phone.

Not with the same meaning.

• w telefonie = in the phone / inside the phone
• do telefonu = into the phone / to the phone

If your focus is the location where the data ends up, w telefonie is natural.

If you said zapisuję dane do telefonu, it might be understood as I save data into the phone, and in some contexts that can work, but it sounds more directional and less neutral.
For the simple idea of data being stored on/in the phone, w telefonie is the most straightforward choice.

The word order can change. Polish word order is more flexible than English, although different orders can change emphasis.

Neutral order:

• Zapisuję dane w telefonie.

Other possible orders:

• Dane zapisuję w telefonie.
  Emphasis on dane
• W telefonie zapisuję dane.
  Emphasis on w telefonie
• Zapisuję w telefonie dane.
  Also possible, though a bit less neutral in many contexts

So the original sentence is a very natural, neutral order, but it is not the only grammatically correct one.

Usually, no.

Polish normally drops subject pronouns when they are clear from the verb ending.

• Zapisuję already means I am saving / I save
• so ja is unnecessary in most situations

You might include ja only for emphasis or contrast:

• Ja zapisuję dane w telefonie, a on w komputerze.
  = I save the data on the phone, and he does it on the computer.

So:

• Zapisuję dane w telefonie. = normal
• Ja zapisuję dane w telefonie. = more emphatic

It can mean several related things, depending on context.

zapisywać / zapisać can mean:

• to write down
• to note down
• to record
• to save

In a sentence with dane and w telefonie, many learners will naturally interpret it as:

• I save data on/in the phone

But in another context, it could be more like:

• I write information down in my phone
• I record data in my phone

So the exact English verb depends on the situation.

A rough pronunciation guide:

• zapisuję ≈ zah-pee-SOO-yeh
• dane ≈ DAH-neh
• w ≈ like English v
• telefonie ≈ teh-leh-FOH-nyeh

A few helpful notes:

• w in Polish is pronounced like English v
• j is pronounced like English y
• ę in zapisuję is often pronounced very lightly at the end, roughly like eh with nasal coloring; in normal speech it may sound almost like e
• nie in telefonie sounds roughly like nye

So the whole sentence sounds approximately like:

zah-pee-SOO-yeh DAH-neh v teh-leh-FOH-nyeh

Sometimes, yes, but the meaning shifts a little.

• dane = data
• informacje = information

These overlap, but they are not always interchangeable.

Use dane especially for:

• technical data
• stored data
• personal data
• digital or system-related data

Use informacje more for:

• information in a general sense
• facts, details, news, content

So with phones, files, or digital storage, dane is often the more natural choice.