Ті, хто мають нагадування в телефоні, приходять вчасно.

Ті means those. In this sentence, it works like the start of the expression Ті, хто... = Those who...

So:

• Ті = those
• хто = who

Together, Ті, хто мають нагадування в телефоні means Those who have reminders on/in their phone.

This is a very common Ukrainian pattern:

• Ті, хто знають... = Those who know...
• Ті, хто працюють... = Those who work...

The comma separates the main part of the sentence from the relative clause.

• Ті = the main word: those
• хто мають нагадування в телефоні = the clause describing which those

So Ukrainian writes:

• Ті, хто мають нагадування в телефоні, приходять вчасно.

This is similar to English Those who have reminders..., but Ukrainian punctuation is stricter here and uses commas around the хто... clause.

Here хто means who.

In Ukrainian, хто can mean:

• who in questions: Хто це? = Who is this?
• who / the one who / those who in relative clauses: Ті, хто... = Those who...

In your sentence, it introduces the group being described:

• ті, хто мають нагадування = those who have reminders

This is a very common learner question.

Grammatically, хто itself looks singular, but in a phrase like Ті, хто... the real meaning is plural: those who... So the verb is often plural to agree with the idea of multiple people.

That is why you see:

• Ті, хто мають... = Those who have...

and not usually:

• Ті, хто має...

So:

• мають = they have
• it matches the plural idea of ті = those

You may sometimes encounter singular agreement with хто in some contexts, but with Ті, хто... plural agreement like мають, приходять, знають is very natural and common.

Actually, нагадування can be either singular or plural depending on context, because neuter nouns of this type often have the same form in:

• nominative singular
• accusative singular
• nominative plural
• accusative plural

Here, because the sentence means have reminders, нагадування is understood as plural.

So:

• нагадування = reminder / reminders

You know which one is intended from context.

Compare:

• Я створив нагадування. = I created a reminder / reminders.
• У мене є нагадування. = I have a reminder / reminders.

Literally, в телефоні means in the phone.

In natural English, we would often say:

• on the phone
• in their phone

Ukrainian commonly uses в + locative for something contained inside a device, app, system, account, etc.

So:

• в телефоні = in/on the phone
• в комп’ютері = in the computer
• в додатку = in the app

Even if English prefers on the phone, Ukrainian often uses в телефоні.

телефоні is in the locative case after the preposition в.

Basic form:

• телефон = phone

After в when it means location, you usually use the locative:

• в телефоні = in the phone

So the ending changes:

• телефон → телефоні

This is a normal pattern:

• в місті = in the city
• в будинку = in the house
• в телефоні = in the phone

Приходять means come / arrive.

In this sentence, it means that these people arrive on time.

• приходять is from приходити = to come, to arrive
• вчасно = on time

So:

• приходять вчасно = come on time / arrive on time

Why not йдуть?

• йдуть means go / are going / walk
• it focuses more on movement itself, not arrival

Why not приїжджають?

• приїжджають means arrive by transport / come by vehicle
• too specific here

So приходять is the natural general choice.

Вчасно means on time, in time, or punctually, depending on context.

In your sentence:

• приходять вчасно = they arrive on time

Related words:

• завчасно = ahead of time, in advance, earlier than necessary
• своєчасно = timely, at the proper time, often a bit more formal

Examples:

• Він прийшов вчасно. = He arrived on time.
• Вона зробила це завчасно. = She did it in advance.
• Ми своєчасно відреагували. = We responded in a timely manner.

For everyday punctuality, вчасно is the most common word.

Yes, the subject is understood from the earlier phrase:

• Ті, хто мають нагадування в телефоні

Ukrainian often omits subject pronouns when the verb ending already makes the meaning clear or when the subject has already been stated.

So Ukrainian does not need:

• Ті, хто мають нагадування в телефоні, вони приходять вчасно.

That would usually sound unnecessary or heavy here.

The verb ending -ять already shows plural:

• приходять = they come/arrive

So the sentence is complete without вони.

Yes, absolutely.

Although the structure is literally Those who have reminders in their phone come on time, natural English could also be:

• People who have reminders on their phones arrive on time.
• Those who keep reminders on their phones arrive on time.
• People with phone reminders arrive on time.

The Ukrainian sentence is general and descriptive, so several natural English translations are possible.

Yes, literally it is singular: in the phone.

But Ukrainian often uses the singular in this kind of generic statement, where each person is understood to have their own phone.

So:

• Ті, хто мають нагадування в телефоні... naturally means
• Those who have reminders in their phone / on their phones...

English often prefers plural phones in this situation, but Ukrainian singular is completely normal because it refers to the phone belonging to each person in the group.