Jeśli nie mogę odebrać telefonu, oddzwonię po pracy.

Both jeśli and jeżeli mean if and are usually interchangeable.

• Jeśli is a bit more common in everyday speech.
• Jeżeli can sound slightly more formal or careful.

So:

• Jeśli nie mogę odebrać telefonu, oddzwonię po pracy.
• Jeżeli nie mogę odebrać telefonu, oddzwonię po pracy.

Both are correct.

After móc (can / be able to), Polish normally uses the infinitive.

So:

• mogę odebrać = I can answer / pick up
• nie mogę odebrać = I can’t answer / pick up

You do not use a conjugated verb after mogę in this structure.

Compare:

• Mogę przyjść. = I can come.
• Mogę zadzwonić później. = I can call later.

Odebrać telefon means to answer / pick up the phone.

In everyday Polish, this is the standard expression for answering a phone call.

Related expressions:

• odebrać telefon = answer the phone
• nie odebrać telefonu = not answer the phone
• dzwonić = to call / ring
• oddzwonić = to call back

So the sentence means that if the speaker cannot answer the phone now, they will call back later.

Because after odebrać in this negative structure, Polish often uses the genitive instead of the accusative.

Here:

• odebrać telefon = to answer the phone
• nie mogę odebrać telefonu = I can’t answer the phone

This is a very common pattern with negation in Polish: the direct object often changes to the genitive.

Compare:

• Mam czas. = I have time.
• Nie mam czasu. = I don’t have time.

And similarly:

• Odbiorę telefon. = I’ll answer the phone.
• Nie mogę odebrać telefonu. = I can’t answer the phone.

In careful standard Polish, telefonu is the expected form here because of negation.

So:

• nie mogę odebrać telefonu is the standard version.

You may sometimes hear variation in modern spoken Polish with other verbs, but for learners it is best to remember:

• negation often triggers the genitive
• with this sentence, telefonu is the natural and correct choice

Because oddzwonić is a single verb meaning to call back.

Its infinitive is:

• oddzwonić = to return a call / call back

And oddzwonię is the 1st person singular future form:

• oddzwonię = I will call back

This is not od + dzwonię as separate words. It is one complete verb.

Good question. In Polish, many perfective verbs use present-tense-looking forms to express the future.

Oddzwonić is a perfective verb, so:

• oddzwonię literally has present-style endings,
• but its meaning is future: I will call back.

Compare:

• dzwonię = I am calling / I call
• oddzwonię = I will call back

This happens because perfective verbs do not normally have a true present meaning in the same way imperfective verbs do.

These are related but not identical.

• dzwonić = to call / to be calling; imperfective
• zadzwonić = to call / to give a call; perfective
• oddzwonić = to call back; perfective

Examples:

• Dzwonię do mamy. = I’m calling my mum.
• Zadzwonię jutro. = I’ll call tomorrow.
• Oddzwonię później. = I’ll call back later.

In your sentence, oddzwonię is used because the meaning is specifically returning the missed call.

Because the preposition po requires a particular case here: the locative.

• praca = work
• po pracy = after work

So the noun changes form after po.

Other examples:

• po obiedzie = after lunch
• po szkole = after school
• po spotkaniu = after the meeting

This is a set phrase you should learn as a chunk: po pracy.

Usually po pracy means after work, in the everyday sense of after my workday / when I finish work.

In this sentence:

• oddzwonię po pracy = I’ll call back after work

It does not usually mean after I finish a specific task. For that, Polish would often use a more specific phrase, depending on the situation.

Yes. Polish word order is more flexible than English, although some versions sound more natural in certain contexts.

The original sentence:

• Jeśli nie mogę odebrać telefonu, oddzwonię po pracy.

Other possible orders:

• Oddzwonię po pracy, jeśli nie mogę odebrać telefonu.
• Jeśli nie mogę odebrać telefonu, po pracy oddzwonię.

The original version is very natural and neutral. Changing the order can shift emphasis slightly:

• oddzwonię po pracy puts focus on the promise to call back
• po pracy oddzwonię gives a little more emphasis to after work

Not in the same meaning.

• jeśli = if
• gdy = when
• kiedy = when

Your sentence is conditional: if I can’t answer the phone, I’ll call back after work.

So jeśli is the right choice.

If you said:

• Gdy nie mogę odebrać telefonu, oddzwaniam po pracy.

that would sound more like a habitual statement: When I can’t answer the phone, I call back after work.

So the meaning changes.

Because in Polish, a subordinate clause introduced by words like jeśli is separated by a comma.

So:

• Jeśli nie mogę odebrać telefonu, oddzwonię po pracy.

This is standard punctuation in Polish.

The same happens with many similar connectors, for example:

• Kiedy wrócę, zadzwonię.
• Jeżeli będzie czas, przyjdę.

It is fairly neutral and natural. You could use it in many situations:

• to a friend
• to a colleague
• in a text message
• in everyday spoken language

It is polite enough for normal use, though in a very formal setting you might choose slightly more formal wording depending on context.

A very conversational alternative might be:

• Jeśli nie odbiorę, oddzwonię po pracy.

That version is shorter and also very common.

They are similar, but not exactly the same.

• Jeśli nie mogę odebrać telefonu = If I can’t answer the phone

  • this emphasizes ability / possibility
  • maybe you are busy, in a meeting, driving, etc.

• Jeśli nie odbiorę telefonu = If I don’t answer the phone

  • this focuses more on the event itself
  • it does not explicitly say why

Both are natural, but your original sentence suggests: if I’m unable to answer, I’ll call back after work.

In this context, it effectively refers to the call, even though the literal word is phone.

That is normal in both Polish and English:

• answer the phone
• odebrać telefon

You are not really answering the device itself; you are answering the incoming call. But Polish uses this standard expression, just as English does.