Якщо дверний дзвінок не працює, я телефоную Олені.

Якщо means if. It introduces the condition:

Якщо дверний дзвінок не працює = If the doorbell doesn’t work

So the sentence has two parts:

• the condition: Якщо дверний дзвінок не працює
• the result: я телефоную Олені

Because Ukrainian normally separates a subordinate clause from the main clause with a comma. Since якщо introduces a subordinate clause, the comma is required:

Якщо дверний дзвінок не працює, я телефоную Олені.

You would also use a comma if the order were reversed:

Я телефоную Олені, якщо дверний дзвінок не працює.

It literally means door bell.

• дверний = door-, related to a door
• дзвінок = bell, ring, or doorbell depending on context

So дверний дзвінок is the normal way to say doorbell.

Because Ukrainian often uses an adjective where English uses a noun modifying another noun.

• двері = door / doors
• дверний = door-related

So instead of something like door bell with two nouns side by side, Ukrainian says дверний дзвінок, with an adjective + noun structure.

Also, дверний matches дзвінок in gender, number, and case:

• masculine
• singular
• nominative

Because працювати is the normal verb for something functioning or not functioning.

• працює = works / is working / functions
• не працює = doesn’t work / isn’t working

This is very common for machines, devices, systems, and appliances in Ukrainian. English learners sometimes expect a verb like do or make, but Ukrainian normally uses працювати here.

Also, не is written separately from the verb:

• не працює
• not one word

Працює is the 3rd person singular present form of працювати.

That means it matches the subject дверний дзвінок, which is singular:

• дверний дзвінок працює = the doorbell works
• дверний дзвінок не працює = the doorbell doesn’t work

Телефоную is the 1st person singular present form of телефонувати.

So:

• телефоную = I call / I am calling by phone

The ending shows the subject, which is why Ukrainian often does not need the pronoun я.

Because телефонувати usually takes the dative case: you phone to someone.

So:

• Олена = nominative, the basic dictionary form
• Олені = dative, used after телефонувати

This is one of the most important things to notice in the sentence:

• Я телефоную Олені. = I call Olena.

Even though English does not show this with a special ending, Ukrainian does.

Yes, you could.

Both are common:

• телефоную Олені
• дзвоню Олені

In modern everyday speech, both can mean I call Olena.
Телефонувати is more explicitly to phone, while дзвонити originally relates to ringing, but it is also widely used for phone calls.

Both normally take the dative:

• телефоную Олені
• дзвоню Олені

Not always. Ukrainian often drops subject pronouns because the verb ending already shows the person.

So both are possible:

• Якщо дверний дзвінок не працює, я телефоную Олені.
• Якщо дверний дзвінок не працює, телефоную Олені.

Including я can add clarity, contrast, or emphasis, but it is not grammatically required.

It most naturally describes a habitual or general situation:

If the doorbell doesn’t work, I call Olena.

Both verbs are in the present tense, but the meaning is not necessarily about this exact moment. It is more like a rule, habit, or repeated situation.

If you wanted a more clearly one-time future meaning, Ukrainian would often change the main verb:

• Якщо дверний дзвінок не працює, я зателефоную Олені.
• If the doorbell doesn’t work, I’ll call Olena.

So the original sentence sounds like a regular practice or general response.

Yes. Ukrainian word order is fairly flexible.

The version in your sentence is very natural:

Якщо дверний дзвінок не працює, я телефоную Олені.

But you can also say:

Я телефоную Олені, якщо дверний дзвінок не працює.

The meaning stays basically the same. The difference is mostly about emphasis and flow, not core grammar. The original version puts the condition first, which is very common.