फोन बज रहा है।

A quick breakdown:

• फोन = phone
• बज = the verb stem from बजना, meaning to ring / to sound
• रहा = marks an ongoing action
• है = is

So the structure is basically:

• phone + ring + ongoing + is

That is why the sentence means The phone is ringing.

Because Hindi normally prefers Subject–Object–Verb order, and the verb phrase usually comes at the end.

So:

• फोन = subject
• बज रहा है = verb phrase

In English, you say The phone is ringing.
In Hindi, the natural order is more like Phone ringing is.

You should not translate Hindi word-for-word into English order.

These two forms mean different things:

• बज रहा है = is ringing right now, at this moment
• बजता है = rings in general, habitually, or regularly

Examples:

• फोन बज रहा है। = The phone is ringing.
• यह फोन बहुत तेज़ बजता है। = This phone rings very loudly.
• अलार्म रोज़ छह बजे बजता है। = The alarm rings every day at six.

So रहा है gives the idea of an action in progress.

बजना is the dictionary form, the infinitive: to ring.

When Hindi makes the progressive form, it does not use the full infinitive. It uses the verb stem:

• बजना → remove -ना → बज
• then add रहा / रही / रहे
• then add a form of होना such as है

So:

• बजना → बज रहा है

This is very common in Hindi:

• करना → कर रहा है
• सोना → सो रहा है
• आना → आ रहा है

It marks the progressive aspect, meaning the action is ongoing.

You can think of it like this:

• रहा = ongoing/in progress
• है = is

Together, रहा है works like English is ...-ing, but Hindi forms it differently.

So:

• बज रहा है = is ringing

A useful point: है alone does not mean is ringing.
The sense of -ing comes from रहा, not from है.

Because रहा / रही / रहे agrees with the noun.

Here, फोन is normally treated as masculine singular, so Hindi uses:

• रहा

Compare:

• फोन बज रहा है। = The phone is ringing.
• घंटी बज रही है। = The bell is ringing.
  
  • घंटी is feminine, so रही
• फोन बज रहे हैं। = The phones are ringing.
  
  • plural, so रहे

So the form changes according to gender and number.

Yes, in ordinary Hindi, फोन is usually treated as masculine.

That is why you get:

• फोन बज रहा है
• not फोन बज रही है

Loanwords from English still have to behave like Hindi nouns, so speakers assign them a gender. For फोन, masculine is the normal choice.

This is a very common question.

• बजना = to ring / to sound / to play by itself
• बजाना = to ring / to play something, causing it to sound

So:

• फोन बज रहा है। = The phone is ringing.
  
  • the phone is making the sound
• मैं घंटी बजा रहा हूँ। = I am ringing the bell.
  
  • I am causing the bell to ring
• वह गिटार बजा रहा है। = He is playing the guitar.

So in your sentence, बजना is correct because the phone is the thing producing the sound.

Because Hindi does not normally use articles like a, an, and the the way English does.

So:

• फोन can mean the phone or a phone, depending on context

In this sentence, the context makes it natural to understand the phone.

This is very normal in Hindi, and learners should get used to not looking for a separate word for the.

In standard Hindi, you should say:

• फोन बज रहा है।

Leaving out है may happen in very casual speech, poetry, dialogue, or headlines, but it sounds incomplete for a learner's normal usage.

So as a rule:

• Use the full form: बज रहा है

That is the safest and most natural choice.

In modern Hindi, many people write फोन even though the word is borrowed from English phone.

In actual pronunciation, most speakers say something close to:

• fon

So even without the dot under फ़, the intended sound is usually still f in this common word.

The whole sentence is approximately:

• fon baj rahaa hai

That said, pronunciation varies a little by speaker and region.

Yes, but the grammar changes because घंटी is feminine.

Compare:

• फोन बज रहा है। = The phone is ringing.
• घंटी बज रही है। = The bell is ringing.

So the main verb stays the same idea, but रहा changes to रही to match the feminine noun घंटी.