Если мой телефон снова сломается, мне придётся купить новый.

In Russian, a real future condition normally uses the future after если.

So Russian says:

• Если мой телефон снова сломается... = If my phone breaks again...

Even though English uses a present form (breaks), Russian uses a future form because the event is still in the future.

This is very normal in Russian:

• Если будет дождь, мы останемся дома.
  If it rains, we’ll stay home.

• Если он придёт, я скажу ему.
  If he comes, I’ll tell him.

So если + future is the standard pattern for likely/real future situations.

Because сломаться means to break down / to get broken (intransitive), while сломать means to break something (transitive).

Compare:

• Я сломал телефон.
  I broke the phone.
  Here, someone caused the damage.

• Телефон сломался.
  The phone broke / stopped working.
  Here, the phone itself is the thing that stopped working.

In your sentence, the phone is not breaking something else. The phone itself stops working, so Russian uses сломаться.

The form сломается is:

• 3rd person singular
• future
• from the perfective verb сломаться

So it literally means will break / will break down.

The -ся is part of the verb сломаться. In this case, it helps form a verb meaning to become broken / to break down.

For learners, the easiest way to think of it is:

• сломать = to break something
• сломаться = to break / to break down

This does not always translate as a literal reflexive like himself or itself in English. Often, -ся just creates a different verb with a different meaning.

So here, сломается does not mean will break itself in a strange literal sense. It simply means will break down.

Because придётся comes from придтись / приходиться, which is used in an impersonal construction meaning to have to, to be forced to, or to end up having to.

Russian expresses this idea like this:

• мне придётся = I will have to
• тебе придётся = you will have to
• нам придётся = we will have to

The person who is affected goes in the dative case:

• мне = to me
• тебе = to you
• ему = to him

So the structure is not literally I will have to, but more like:

• To me, it will come to be necessary...

That is why Russian uses мне придётся купить новый rather than a personal form like я придусь, which would be wrong here.

Because the construction придётся + infinitive takes the person in the dative.

So:

• мне придётся = I’ll have to
• тебе придётся = you’ll have to
• ему придётся = he’ll have to

This is common in Russian with impersonal expressions of necessity, possibility, comfort, age, and so on.

Compare:

• Мне нужно уйти. = I need to leave.
• Мне нельзя здесь курить. = I’m not allowed to smoke here.
• Мне двадцать лет. = I am twenty years old.

So мне is dative because Russian treats the idea as something that applies to the person.

Both can mean I will have to, but the nuance is a bit different.

• мне придётся = I’ll have to / it looks like I’ll have to / I’ll end up having to
• я должен буду = I will be obliged to / I will have to in a more direct, personal, duty-based way

In this sentence, мне придётся купить новый sounds very natural because it suggests necessity caused by circumstances:

• If the phone breaks again, the situation will force me to buy a new one.

Using я должен буду купить новый is possible, but it can sound more like obligation or duty, and here the idea is more about practical necessity than moral obligation.

So придётся is a very good choice.

After придётся, Russian normally uses an infinitive to say what someone will have to do.

So the pattern is:

• мне придётся + infinitive

Examples:

• Мне придётся уйти.
  I’ll have to leave.

• Нам придётся подождать.
  We’ll have to wait.

• Ему придётся купить новый телефон.
  He’ll have to buy a new phone.

In your sentence:

• мне придётся купить новый

The infinitive купить tells us what action will be necessary.

Because купить is perfective, and here Russian is talking about one complete future action: buying a new phone.

• купить = to buy (completed, single result)
• покупать = to buy / to be buying (process, repeated action, or general activity)

In this sentence, the point is the result:

• If the phone breaks again, I’ll have to buy a new one.

That is a one-time completed action, so купить is the natural choice.

If you used покупать, it would sound more like a process or repeated activity, which does not fit as well here.

Because Russian often leaves out a noun when it is obvious from context.

Here, новый means:

• a new one
• specifically, a new phone

The omitted noun is телефон, and the adjective stays in the form that matches it:

• новый = masculine singular nominative/accusative form, matching телефон

So:

• купить новый = to buy a new one
• full version: купить новый телефон

This is very common in Russian, just like in English:

• I need a new one.
• Мне нужен новый.

Because it refers to the omitted noun телефон, which is masculine.

Russian adjectives must agree with the noun they describe in:

• gender
• number
• case

Since телефон is masculine singular, the adjective is also masculine singular:

• новый телефон
• купить новый = buy a new one (with телефон understood)

If the omitted noun were feminine, neuter, or plural, the adjective would change:

• новая = feminine
• новое = neuter
• новые = plural

It is in the nominative case.

That is because мой телефон is the subject of the verb сломается:

• мой телефон сломается = my phone will break

The subject of a sentence is normally in the nominative.

Both words are nominative masculine singular:

• мой = nominative masculine singular
• телефон = nominative singular

Because снова means again, and it naturally modifies the verb:

• снова сломается = break again

Its placement here is very normal and neutral.

You may also hear similar adverbs in this position:

• опять сломается
• снова сломается

Both снова and опять can mean again, though опять is often a bit more conversational and can sometimes sound slightly more emotional, depending on context.

So снова here simply means that this is not the first time the phone has broken.

Yes. Russian word order is more flexible than English, although the neutral order here is perfectly natural:

• Если мой телефон снова сломается, мне придётся купить новый.

You could also hear variations like:

• Если снова сломается мой телефон, мне придётся купить новый.
• Мне придётся купить новый, если мой телефон снова сломается.

These mean basically the same thing, but the emphasis can shift slightly.

The original version is a very natural, standard way to say it.

Yes, absolutely.

• снова = again
• опять = again

Both are common and natural:

• Если мой телефон снова сломается...
• Если мой телефон опять сломается...

In many contexts they are interchangeable. Very roughly:

• снова can sound a little more neutral
• опять can sound a little more conversational, and sometimes more emotional or annoyed

If your phone keeps breaking, опять might sound especially natural in speech.

It usually sounds like a real future possibility.

The structure:

• Если ... сломается, ... придётся ...

suggests:

• this could really happen in the future
• and if it does, there will be a practical consequence

Russian often uses this kind of sentence for ordinary real-life conditions. It is not a contrary-to-fact hypothetical like English If my phone were to break... or If my phone had broken...

So the sentence feels like:

• If my phone breaks again, I’ll have to buy a new one.

A normal, realistic future scenario.