Obejrzeliśmy tylko połowę odcinka, bo zadzwonił telefon.

Because Polish makes a strong distinction between perfective and imperfective verbs.

• obejrzeliśmy = perfective past, from obejrzeć
• oglądaliśmy = imperfective past, from oglądać

Here, obejrzeliśmy tylko połowę odcinka presents the action as a completed chunk: we got as far as half of the episode, and that amount is treated as finished.

If you said oglądaliśmy tylko połowę odcinka, it would sound more like we were watching only half of the episode or we watched only half with more focus on the ongoing process, not on reaching that half as a completed result.

So obejrzeliśmy fits well because the sentence reports a finished outcome.

Because połowę is the accusative form of połowa.

The verb obejrzeć takes a direct object, and direct objects are often in the accusative in Polish.

• nominative: połowa = half
• accusative: połowę

So:

• Obejrzeliśmy połowę... = We watched half...

That is why połowa changes to połowę.

Because after words like połowa (half), Polish usually puts the thing being measured in the genitive.

So:

• połowa odcinka = half of an episode
• połowę odcinka = half of an episode, with połowę in accusative because it is the object of the verb

Here:

• odcinek = nominative
• odcinka = genitive

This is very common in Polish with quantity expressions:

• szklanka wody = a glass of water
• kilo jabłek = a kilo of apples
• połowa filmu = half of the film

It is a two-part structure:

• połowę = accusative, because it is the direct object of obejrzeliśmy
• odcinka = genitive, because it depends on połowa / połowę

So the whole phrase works like:

• we watched
  • half
    • of the episode

A useful way to think about it is: the verb governs połowę, and połowę governs odcinka.

Because Polish usually does not need subject pronouns when the verb ending already shows the person.

• obejrzeliśmy already means we watched
• the ending -liśmy tells you it is we in the past

So my obejrzeliśmy... is possible, but unnecessary unless you want emphasis, for example:

• My obejrzeliśmy tylko połowę odcinka, a oni cały. = We watched only half of the episode, and they watched the whole one.

That Polish sentence is perfectly natural. Literally, it is also the phone rang:

• zadzwonił = rang
• telefon = phone

Polish often allows more flexible word order than English. Here, putting the verb first can sound very natural in narration, especially when a new event suddenly happens.

So:

• bo zadzwonił telefon = because the phone rang
• bo telefon zadzwonił is also grammatical, but it may sound a bit more neutral or slightly more focused on telefon

In many contexts, the verb-first version sounds smoother.

Because it agrees with telefon, which is a masculine singular noun.

In the past tense, Polish verbs agree in gender and number with the subject.

• telefon is masculine singular
• so the verb is zadzwonił

Compare:

• zadzwonił telefon = the phone rang
• zadzwoniła komórka = the mobile phone rang
• zadzwoniły telefony = the phones rang

It is in the nominative, because it is the subject of the verb zadzwonił.

This can confuse English speakers because in English phone comes before the verb most of the time, while in Polish the subject can come after the verb without changing its role.

So in:

• zadzwonił telefon

telefon is still the subject, not an object.

Because tylko means only, and here it modifies połowę odcinka.

• Obejrzeliśmy tylko połowę odcinka = We watched only half of the episode

Placing tylko right before the phrase it limits is very common and clear.

Polish word order is flexible, so other placements are possible, but they can change the emphasis:

• Tylko obejrzeliśmy połowę odcinka... would sound odd in most contexts
• Obejrzeliśmy połowę odcinka tylko dlatego, że... would mean something else because now tylko is linked to dlatego

So in this sentence, tylko połowę is the natural choice.

Yes. Polish word order is flexible, though not random. You can move things around to change emphasis.

For example:

• Obejrzeliśmy tylko połowę odcinka, bo zadzwonił telefon.
  Neutral and natural.

• Tylko połowę odcinka obejrzeliśmy, bo zadzwonił telefon.
  Stronger emphasis on only half of the episode.

• Bo zadzwonił telefon, obejrzeliśmy tylko połowę odcinka.
  More emphasis on the reason.

The original version is the most straightforward and natural for ordinary speech.

Yes, ponieważ is possible, but bo is more common in everyday speech.

• bo = because
• ponieważ = because / since, usually a bit more formal or bookish

So:

• Obejrzeliśmy tylko połowę odcinka, bo zadzwonił telefon.
  Very natural spoken Polish.

• Obejrzeliśmy tylko połowę odcinka, ponieważ zadzwonił telefon.
  Also correct, but slightly more formal.

It usually means it rang as a completed event. Since zadzwonić is perfective, it presents the ringing as a whole event, often sudden or punctual.

In context, it often corresponds well to English rang:

• zadzwonił telefon = the phone rang

If you wanted to describe ongoing ringing, Polish would more likely use an imperfective verb, depending on the context.

So here the idea is: the ringing happened, and that event interrupted the watching.

A rough guide for an English speaker:

o-bey-zhe-LI-shmy

A few important points:

• rz here sounds like the zh in measure
• ł sounds like English w
• ś is a soft sh-like sound
• my at the end is not like English my; it is closer to mih

So -liśmy sounds roughly like LEE-shmih.

This word is a bit of a mouthful even for learners, so it helps to break it up:

• o-bej-rze-li-śmy

Usually yes, or at least one episode understood from context.

• odcinka has no article because Polish does not use a/the
• whether it means an episode or the episode depends on context

In a likely real-life context, this would usually mean the episode that we were watching.

So English needs an article, but Polish does not.

Yes, that is also correct, but it means something slightly different.

• Obejrzeliśmy tylko połowę odcinka... focuses on the result: we got through only half.
• Przerwaliśmy oglądanie... focuses on the interruption itself: we stopped watching.

So both are natural, but the original sentence emphasizes how much of the episode was watched before the phone rang.