Na početku sastanka uvijek isključim mobitel.

Because na početku means at the beginning and uses the locative case after na to show a location in time.

• početak = beginning
• na početku = at the beginning

By contrast, na početak would use the accusative and usually suggest movement to the beginning, which does not fit here.

So:

• na početku sastanka = at the beginning of the meeting

Because it depends on početak.

The basic noun is:

• sastanak = meeting

After a noun like početak (beginning), Croatian often uses the genitive to mean of something:

• početak sastanka = the beginning of the meeting

So sastanka is the genitive singular of sastanak.

This is a very common learner question because it involves aspect.

• isključiti = perfective, to switch off / turn off as a completed action
• isključivati / isključujem = imperfective, focusing more on the process or repeated activity

In this sentence, isključim sounds natural because the speaker means a complete action that happens each time: at the beginning of a meeting, I turn off my phone.

So the sentence presents each occasion as a finished event.

A learner should know this nuance:

• uvijek isključim mobitel = each time, I switch it off
• uvijek isključujem mobitel = less natural here; it can sound more like focusing on the repeated habit itself rather than the single completed action on each occasion

In everyday Croatian, the perfective form works well in this type of repeated context.

Because Croatian aspect and tense interact differently from English.

Formally, isključim is present tense, 1st person singular of a perfective verb. Perfective present forms often refer to the future, but not always. In a sentence with uvijek (always) and a habitual context, it can describe something that happens regularly.

So here:

• uvijek isključim mobitel = I always turn off my phone

The idea is: whenever the situation happens, the action is completed.

It is in the accusative singular, which is the normal case for the direct object of the verb.

• mobitel = mobile phone / cellphone
• isključiti mobitel = to turn off a phone

Since mobitel is a masculine inanimate noun, its accusative singular looks the same as the nominative singular:

• nominative: mobitel
• accusative: mobitel

That is why the form does not change.

Yes.

• mobitel specifically means mobile phone / cellphone
• telefon can mean phone more generally, and in context it can also mean a mobile phone

So these are both possible:

• Na početku sastanka uvijek isključim mobitel.
• Na početku sastanka uvijek isključim telefon.

In Croatia, mobitel is very common when you want to be specific about a mobile phone.

Yes, Croatian word order is fairly flexible, although some orders sound more natural than others.

The given sentence:

• Na početku sastanka uvijek isključim mobitel.

is perfectly natural.

You could also hear:

• Uvijek isključim mobitel na početku sastanka.
• Mobitel uvijek isključim na početku sastanka.

The meaning stays basically the same, but the focus changes slightly.

• Starting with Na početku sastanka highlights the time point.
• Starting with Uvijek emphasizes the regularity.
• Moving mobitel earlier can emphasize the object.

Croatian often uses word order for emphasis more than English does.

Because Croatian does not have articles like English a/an or the.

So:

• sastanak can mean a meeting or the meeting
• mobitel can mean a phone or the phone

The exact meaning is understood from context.

In this sentence, English would usually say:

• At the beginning of the meeting, I always turn off my phone.

Croatian simply does not need articles to express that.

It is used for both, and here it is used in a time expression.

Examples:

• na početku ulice = at the beginning of the street
• na početku filma = at the beginning of the film
• na početku sastanka = at the beginning of the meeting

So Croatian treats the beginning as a kind of point or position, whether literal or abstract.

A rough guide for an English speaker is:

• is-klyoo-cheem

A few useful points:

• lj is a single Croatian sound, something like the lli in some pronunciations of million
• č sounds like ch in church
• stress is not usually marked in normal writing, so learners often just imitate native audio

You do not need perfect stress right away; getting lj and č reasonably close is the main thing.

Not exactly.

• isključiti mobitel means to switch off / turn off the phone
• utišati mobitel means to silence / mute the phone

So if you only mean putting it on silent mode, Croatian would normally use a different verb.

That makes isključim quite specific: the phone is being turned off, not just muted.