Этот телефон мой.

In Russian, the verb to be is usually omitted in the present tense.

So Russian says:

Этот телефон мой
literally: This phone mine

But it means This phone is mine.

This is completely normal. In the past or future, forms of быть do appear:

Этот телефон был мой = This phone was mine
Этот телефон будет мой = This phone will be mine

Because телефон is a masculine singular noun, and этот has to agree with it.

Russian words like this change form depending on gender and number:

• этот = masculine
• эта = feminine
• это = neuter
• эти = plural

Since телефон is masculine, you say этот телефон.

Compare:

• этот телефон = this phone
• эта книга = this book
• это окно = this window
• эти телефоны = these phones

For the same reason: мой agrees with the noun телефон, not with the speaker.

Since телефон is masculine, the possessive pronoun must also be masculine:

• мой телефон = my phone
• моя книга = my book
• моё окно = my window
• мои ключи = my keys

A common English-speaker mistake is to think the form depends on whether the owner is male or female. It does not. It depends on the grammatical gender of the thing owned.

It is in the nominative case.

In this sentence, телефон is the subject, and мой is also in a nominative-style predicate form. Russian often uses this structure in simple present-tense identity or possession statements:

Этот телефон мой = This phone is mine

So even though English uses is mine, Russian does not need a verb here, and the noun stays in the nominative.

Both can mean roughly the same thing, but the focus is different.

• Этот телефон мой puts emphasis on this phone. It can sound contrastive, like This phone is mine.
• Это мой телефон is often a more neutral way to say This is my phone.

So:

• Этот телефон мой = that specific phone belongs to me
• Это мой телефон = this is my phone

Also note that это in Это мой телефон is not the same as этот.
Это often works like this is / that is, while этот directly modifies a noun: this phone.

Yes, Russian word order is flexible.

The sentence Этот телефон мой is natural and often has a slight emphasis on мой, especially in speech: This phone is mine.

Other possible orders include:

• Мой телефон = My phone
• Телефон мой = The phone is mine / The phone is mine, not someone else’s
• Это мой телефон = This is my phone

The words usually keep the same core meaning, but the emphasis changes.

Russian does not have articles like English the and a/an.

So телефон can mean:

• a phone
• the phone

The exact meaning depends on context.

In Этот телефон мой, the word этот already makes the noun specific, so the meaning is clearly this phone.

Yes, you can, if the context makes it clear which phone you mean.

• Этот телефон мой = This phone is mine
• Телефон мой = The phone is mine / That phone is mine, depending on context

Without этот, the sentence is less specific on its own and often sounds more contrastive.

A simple approximation is:

• мой ≈ moy (like the moy in boy with an m at the start)
• этот ≈ EH-tuht

A few useful notes:

• й in мой sounds like the y sound in boy or toy
• э in этот is like e in met, but more open
• The stress is:
  • э́тот
  • мой (only one syllable, so it is naturally stressed)

Yes, it is completely natural.

A native speaker might use Этот телефон мой when identifying which object belongs to them, especially if there are several phones or some possible confusion.

For example, the sentence can imply a contrast such as:

This phone is mine; that one isn’t.

So it is grammatical, natural, and useful in real conversation.