मेरा पुराना फोन काम नहीं करता; यह सच है।

Because मेरा agrees with फोन, and फोन is treated as masculine singular in Hindi.

• मेरा = my (for masculine singular nouns)
• मेरी = my (for feminine singular nouns)
• मेरे = my (for masculine plural nouns, and in some other grammatical contexts)

So:

• मेरा फोन = my phone
• मेरी किताब = my book
• मेरे दोस्त = my friends

पुराना means old, and it also agrees with फोन.

Since फोन is masculine singular, the adjective takes the masculine singular form:

• पुराना फोन = old phone
• पुरानी किताब = old book
• पुराने फोन = old phones

So मेरा पुराना फोन means my old phone.

Yes, फोन is commonly treated as masculine in standard Hindi.

Many borrowed nouns in Hindi are assigned a grammatical gender, and फोन is usually masculine. That is why you get:

• मेरा फोन
• पुराना फोन
• फोन काम नहीं करता

If it were feminine, these forms would change.

Here, काम करना means to work / to function.

So फोन काम नहीं करता means:

• the phone does not work
• the phone doesn’t function

This is a very common Hindi expression for machines, devices, systems, etc.

Examples:

• यह टीवी काम नहीं करता। = This TV doesn’t work.
• मेरा कंप्यूटर काम नहीं करता। = My computer doesn’t work.

Because the subject is फोन, and फोन is masculine singular.

In this kind of sentence, the verb form agrees with the subject:

• masculine singular: करता
• feminine singular: करती
• masculine plural: करते

So:

• फोन काम नहीं करता। = The phone doesn’t work.
• मशीन काम नहीं करती। = The machine doesn’t work.

In Hindi, नहीं usually comes before the verb phrase element it negates.

So:

• काम नहीं करता = does not work

This is the normal order. For learners, it is easiest to remember the pattern:

subject + object/complement + नहीं + verb

Examples:

• मैं नहीं जानता। = I do not know.
• वह नहीं आता। = He does not come.
• फोन काम नहीं करता। = The phone does not work.

It can, but it does not have to.

Both are possible:

• मेरा पुराना फोन काम नहीं करता।
• मेरा पुराना फोन काम नहीं करता है।

In everyday Hindi, the shorter version without है is very common in this kind of habitual statement.

So the sentence as given is completely natural.

यह means this, but in this sentence it refers to the whole previous statement.

So यह सच है means:

• This is true
• That is true

In English, we often say that’s true even when Hindi uses यह.

So here it is not pointing to a physical object. It is pointing to the fact that my old phone doesn’t work.

Because यह सच है is the standard way to say this is true.

Here सच means truth / true in an idiomatic predicate expression.

• यह सच है। = This is true.
• यह झूठ है। = This is false / a lie.

सच्चा usually means something more like genuine, real, or truthful/honest, depending on context. So यह सच्चा है would not normally mean this is true.

Not grammatically. It is just punctuation linking two closely related clauses.

The sentence could also be written as two sentences:

• मेरा पुराना फोन काम नहीं करता। यह सच है।

Or with a comma in more informal writing. The semicolon simply shows that the second clause comments on the first one.

Yes, a little. It is grammatically correct, but it can sound somewhat emphatic or formal, because you are explicitly saying that is true after already making the statement.

In natural conversation, people might simply say:

• मेरा पुराना फोन काम नहीं करता।
• सच में, मेरा पुराना फोन काम नहीं करता। = Seriously, my old phone doesn’t work.
• हाँ, यह सच है। = Yes, that’s true.

So the given sentence is correct, but the second clause adds emphasis.

Yes. That is another very common way to say my old phone doesn’t work.

Compare:

• फोन काम नहीं करता = the phone doesn’t work / function
• फोन नहीं चलता = the phone doesn’t run / work

Both are natural for devices. काम नहीं करता is very broad and useful, while नहीं चलता is also extremely common in everyday speech.

Yes. Hindi often drops things that are already understood from context.

For example:

• मेरा पुराना फोन काम नहीं करता। यह सच है।
• After that, you could continue with just बहुत पुराना है। = It is very old.

Hindi often relies on context more than English does, especially in conversation.