Telefon jest rozładowany i przez to nie mogę oddzwonić.

Rozładowany literally means discharged, and with a phone it usually means dead or out of battery.

So Telefon jest rozładowany = The phone is dead / The phone’s battery is empty.

It comes from the verb rozładować / rozładowywać, which is used for draining or discharging something, especially a battery.

Both are possible, but they focus on slightly different things.

• Telefon jest rozładowany = The phone is discharged / dead
• Telefon ma rozładowaną baterię = The phone has a dead battery

The sentence you were given is a very natural, compact way to say the phone cannot be used because the battery is empty.

In standard Polish, jest is normally used here because the sentence is saying that the phone is in a certain state:

• Telefon jest rozładowany = The phone is dead

Unlike some other Slavic languages, Polish usually keeps the present-tense form of to be in this kind of sentence.

In very informal speech, especially in short messages, people may omit it:

• Telefon rozładowany

But that is more like a note, message, or very casual shorthand. The full standard sentence is Telefon jest rozładowany.

These forms express different things:

• Telefon jest rozładowany describes a state: the phone is dead
• Telefon się rozładował describes an event/change: the phone ran out of battery or became discharged

So:

• Telefon jest rozładowany = what the phone is like now
• Telefon się rozładował = what happened to it

Both are natural, but they are not exactly the same.

Przez to means because of that, as a result, or due to that.

In this sentence:

• Telefon jest rozładowany i przez to nie mogę oddzwonić
• The phone is dead, and because of that I can’t call back

It links the first idea to its consequence.

Other similar expressions are:

• dlatego = therefore / that’s why
• z tego powodu = for this reason / because of this

Yes, it is natural. It means something like:

• and because of that...
• and as a result...

It explicitly shows that the second part follows from the first.

You could also say:

• Telefon jest rozładowany, dlatego nie mogę oddzwonić.
• Telefon jest rozładowany, więc nie mogę oddzwonić.

These are also very natural.
Przez to sounds a bit like stressing the consequence.

Oddzwonić means to call back or to return a phone call.

It is more specific than just zadzwonić:

• zadzwonić = to call / to make a phone call
• oddzwonić = to call back, after someone called before

So if someone contacted you and you want to return that call, oddzwonić is the natural verb.

The prefix od- often gives the idea of back, in return, or away from. In oddzwonić, it creates the sense of calling back.

So very roughly:

• dzwonić = to ring / call
• oddzwonić = to ring back / call back

This kind of prefix is very common in Polish verbs and often changes the meaning in an important way.

Because the sentence means I am unable to call back, not simply I am not calling back.

• nie mogę oddzwonić = I can’t call back
• nie oddzwaniam = I’m not calling back / I don’t call back

The first expresses lack of ability or possibility, which fits the situation: the phone is dead.

Mogę is the 1st person singular present form of móc = can / be able to.

The subject is understood as I, so:

• nie mogę oddzwonić = I can’t call back

The verb móc is irregular, so its forms need to be learned:

• mogę = I can
• możesz = you can
• może = he/she/it can
• możemy = we can
• możecie = you plural can
• mogą = they can

Because móc works like a modal verb, similar to English can. In Polish, modal verbs are commonly followed by an infinitive.

So:

• mogę oddzwonić = I can call back
• nie mogę oddzwonić = I can’t call back

Other examples:

• Mogę przyjść. = I can come.
• Nie mogę spać. = I can’t sleep.

Oddzwonić is a perfective verb. Normally, perfective verbs do not describe an ongoing present action. However, after modal verbs like móc, Polish often uses a perfective infinitive to talk about being able or unable to complete a single action.

So:

• nie mogę oddzwonić = I can’t call back
  meaning I can’t complete that callback

Its imperfective partner is oddzwaniać, which would suggest repeated or habitual calling back.

In this sentence, the perfective form is very natural because it refers to one concrete callback.

Yes, but the meaning changes slightly.

• nie mogę zadzwonić = I can’t call
• nie mogę oddzwonić = I can’t call back

If the idea is specifically that you are returning someone’s call, oddzwonić is the better choice.

Telefon is in the nominative case because it is the subject of the sentence:

• Telefon jest rozładowany

The phone is the thing being described, so nominative is expected.

Because it agrees with telefon, which is:

• masculine
• singular
• nominative

In Polish, adjectives and adjective-like forms must agree with the noun they describe.

So:

• telefon → masculine singular nominative
• rozładowany → masculine singular nominative

If the noun changed, the form would change too:

• bateria jest rozładowana = feminine
• urządzenie jest rozładowane = neuter

The basic order is:

• Telefon jest rozładowany i przez to nie mogę oddzwonić.

This is natural and clear. But Polish word order is flexible, so you could also say things like:

• Przez to nie mogę oddzwonić, bo telefon jest rozładowany.
• Nie mogę oddzwonić, bo telefon jest rozładowany.

The original version first gives the cause and then the consequence. That is a very normal way to structure the sentence.

It is mostly neutral everyday Polish. Nothing in it is especially formal or especially slangy.

• telefon jest rozładowany is ordinary everyday language
• nie mogę oddzwonić is also natural in normal conversation

In a very casual text message, someone might shorten it, for example:

• Telefon mi się rozładował, nie mogę oddzwonić.

But the given sentence is completely natural and standard.

Sometimes, yes. Przez to often points to a consequence, and quite often that consequence is unpleasant or problematic.

In this sentence, that fits perfectly:

• the phone is dead
• therefore I can’t call back

So the phrase works well because the result is clearly a problem.