Mój telefon jest rozładowany, więc nie mogę oddzwonić.

Because telefon is a masculine singular noun, so the possessive adjective must match it.

• mój = my, for masculine singular
• moja = my, for feminine singular
• moje = my, for neuter singular or non-masculine-personal plural

So:

• mój telefon = my phone
• moja książka = my book
• moje auto = my car

Polish adjectives and possessives agree with the noun in gender, number, and case.

Here telefon is the subject of the sentence, so it stays in the nominative case, which is the basic dictionary form.

• Mój telefon jest rozładowany. = My phone is discharged / dead.

You would use telefonu in other grammatical situations, for example:

• Nie mam telefonu. = I do not have a phone.
  Here telefonu is genitive.

So in this sentence, telefon is nominative because it is the thing being described.

In this sentence, jest is the normal and correct choice because Polish usually keeps być (to be) in the present tense when it links the subject with an adjective.

• Mój telefon jest rozładowany. = My phone is dead.

In casual speech, people sometimes omit jest, especially in very informal styles, but for learners the safe standard is:

• X jest Y

So jest should definitely be learned and used here.

Rozładowany literally means discharged. With devices, it usually means:

• dead
• out of battery
• not charged

So telefon jest rozładowany means the battery has run down.

It comes from the verb rozładować / rozładowywać, meaning to discharge or to unload, depending on context.

For electronics:

• Bateria jest rozładowana. = The battery is dead.
• Telefon jest rozładowany. = The phone is dead / out of battery.

Because it agrees with telefon, which is masculine singular.

Adjective endings change to match the noun:

• masculine singular: rozładowany
• feminine singular: rozładowana
• neuter singular: rozładowane

Examples:

• telefon jest rozładowany
• bateria jest rozładowana
• urządzenie jest rozładowane

This is one of the most important patterns in Polish: adjectives must agree with the noun they describe.

Więc means so, therefore, or thus.

It connects two ideas where the second is a result of the first:

• Mój telefon jest rozładowany, więc nie mogę oddzwonić.
• My phone is dead, so I cannot call back.

It is very common in everyday Polish.

Similar words include:

• dlatego = therefore / that is why
• to = so, then, in more conversational linking

For example:

• Jestem zmęczony, więc idę spać. = I am tired, so I am going to sleep.

Because mogę is the 1st person singular present tense form of móc (to be able to / can).

The pattern is:

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

So:

• nie mogę oddzwonić = I cannot call back

After mogę, Polish uses an infinitive:

• mogę zadzwonić = I can call
• mogę mówić = I can speak
• mogę oddzwonić = I can call back

In Polish, nie is the normal negation word and it goes before the verb.

• mogę = I can
• nie mogę = I cannot

This is the standard pattern:

• robię → nie robię
• mam → nie mam
• wiem → nie wiem

So nie mogę oddzwonić literally means I not-can call back, which in natural English is I can’t call back.

These verbs are related but not identical.

• dzwonić = to call / to be calling
  Often imperfective, more general or ongoing.
• zadzwonić = to call, to make a call
  Perfective: one complete call.
• oddzwonić = to call back / return a call

So in this sentence, oddzwonić is used because the idea is specifically calling someone back.

Examples:

• Muszę zadzwonić do Ani. = I need to call Ania.
• Nie mogę teraz rozmawiać, oddzwonię później. = I can’t talk now, I’ll call back later.

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

So:

• mogę oddzwonić = I can call back
• nie mogę oddzwonić = I cannot call back

This is the same structure as in English:

• I can go
• I can speak
• I can call back

Other examples:

• Mogę pomóc. = I can help.
• Nie mogę przyjść. = I cannot come.

Because Polish often leaves out objects when they are already understood from context.

In English, we often say:

• I can’t call you back
• I can’t call him back

In Polish, if the listener already knows who is meant, you can simply say:

• Nie mogę oddzwonić. = I can’t call back.

If you want to specify the person, you can add it, often with do plus genitive:

• Nie mogę do ciebie oddzwonić. = I can’t call you back.
• Oddzwonię do niego później. = I’ll call him back later.

So the shorter version sounds natural when the person is obvious from the situation.

The given word order is natural and standard:

• Mój telefon jest rozładowany, więc nie mogę oddzwonić.

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

For example, you might hear:

• Nie mogę oddzwonić, bo mój telefon jest rozładowany.
• Mój telefon jest rozładowany, dlatego nie mogę oddzwonić.

All of these are grammatical, but the original version is a very good neutral model for learners.

A rough pronunciation guide:

• mój ≈ mooy
• więc ≈ vyents
• oddzwonić ≈ od-zvaw-neech
• mogę ≈ mo-gheh (with nasal ę at the end, often weakened in normal speech)

A few useful pronunciation notes:

• ó sounds like u
• w sounds like English v
• dzw is a consonant cluster, roughly like dzv
• ć is a soft ch-like sound
• ę is nasal, though in fast speech its pronunciation can vary

You do not need perfect pronunciation immediately, but it helps to notice that Polish spelling is fairly consistent once you learn the sound patterns.