Miałam oddzwonić do mamy, ale telefon był rozładowany i nie było zasięgu.

Because miałam is the past tense, feminine form of mieć for I.

• miałam = I had / I was supposed to said by a woman
• miałem = the same, but said by a man

So this sentence tells us the speaker is female.

In this sentence, miałam oddzwonić means something like:

• I was supposed to call back
• I meant to call back
• I had to call back
  depending on context

This structure often expresses an intention, plan, obligation, or expectation in the past.

So it does not simply mean I had called back. It means the call back was expected or intended, but we later learn it did not happen because the phone was dead and there was no signal.

Because after mieć in this kind of construction, Polish commonly uses the infinitive.

So:

• miałam oddzwonić = I was supposed to call back
• literally: I had to call back / I was to call back

This works similarly to some English patterns like I was supposed to go, where go also stays in a base form.

Oddzwonić means to call back / return a call.

Zadzwonić just means to call / to ring.

So:

• zadzwonić do mamy = to call mum
• oddzwonić do mamy = to call mum back

The prefix od- often adds the idea of back or in return.

Because with the verb dzwonić / oddzwonić, Polish normally uses do + Genitive when you mean to call someone.

So:

• dzwonić do mamy = to call mum
• oddzwonić do mamy = to call mum back

This is just the standard pattern.

Even though English says call someone, Polish says more literally call to someone with do.

Because after do, the noun goes into the Genitive case.

• nominative: mama
• genitive: mamy

So:

• do mamy = to mum / to my mum

This is a very common change for feminine nouns ending in -a.

No, here mamy is the Genitive singular form of mama.

It can look confusing because mamy can also mean:

• we have

But in this sentence, the context makes it clear:

• do mamy = to mum

So it is a noun form, not a verb.

It means the phone was out of battery / discharged / dead.

• telefon = phone
• był = was
• rozładowany = discharged, out of charge

A very natural English translation would be:

• the phone was dead
• the battery was dead

Polish often describes the phone as discharged, not just the battery.

These two forms focus on different things:

• telefon był rozładowany = the phone was dead
  → describes the state
• telefon się rozładował = the phone ran out of battery / discharged itself
  → describes the event/change

In your sentence, the important point is the condition that prevented the speaker from calling, so the state is more natural.

It means:

• there was no signal
• there was no reception
• there was no network coverage

Zasięg is what your phone has when it can connect to the mobile network.

So the second problem in the sentence is not just the dead phone, but also lack of signal.

Because Polish commonly uses być in an impersonal/existential way here:

• był zasięg = there was signal
• nie było zasięgu = there was no signal

This is like English there was rather than the signal was.

Also, after negation, Polish often uses the Genitive:

• zasięg → zasięgu

So nie było zasięgu is the normal pattern.

Because Polish usually does not need subject pronouns when the verb already shows who is doing the action.

Here miałam already tells us:

• person: I
• number: singular
• gender: feminine

So ja would usually be unnecessary unless you want extra emphasis.

Yes, Polish word order is fairly flexible, although some versions sound more natural than others.

For example, you could also say:

• Miałam oddzwonić mamie, ale telefon był rozładowany i nie było zasięgu.
• Ale telefon był rozładowany i nie było zasięgu, więc nie mogłam oddzwonić do mamy.

But the original sentence is very natural. It starts with the speaker’s intention, then explains the reason it was not possible.