फोन एकदम बजा।

Because फोन is usually treated as a masculine singular noun in Hindi, and in this kind of past sentence the verb agrees with it.

• फोन → masculine singular
• so the verb appears as बजा

Compare:

• घंटी बजी। = The bell rang.
  
  • घंटी is feminine, so बजी
• फोन बजा। = The phone rang.
  
  • फोन is masculine, so बजा

It comes from बजना, which means to ring, to sound, or to play (for an instrument, alarm, bell, etc., depending on context).

So:

• बजना = to ring / to sound
• बजा = rang / sounded

Examples:

• अलार्म बजा। = The alarm rang.
• ढोल बजा। = The drum sounded.

Be careful not to confuse it with बजाना, which is usually the causative/transitive form: to play or to make something sound.

• मैं गिटार बजाता हूँ। = I play the guitar.
• फोन बजा। = The phone rang.

Because बजना here is an intransitive verb: the phone itself is doing the ringing; there is no agent performing an action on an object.

In Hindi, ने is typically used with many transitive perfective verbs, especially when someone did something to something else.

Compare:

• राम ने दरवाज़ा खोला। = Ram opened the door.
  
  • transitive → ने appears
• फोन बजा। = The phone rang.
  
  • intransitive → no ने

So फोन is not marked with ने here.

Here एकदम means something like:

• suddenly
• all of a sudden
• abruptly
• sometimes right away, depending on context

In फोन एकदम बजा।, it gives the sense that the phone rang suddenly or all at once.

A very close alternative is अचानक:

• फोन अचानक बजा।
• फोन एकदम बजा।

These are similar, though एकदम can also have other meanings in other contexts, such as completely, totally, or exactly/right away.

Both can occur, but they are a bit different in feel.

• फोन एकदम बजा। = The phone rang suddenly / abruptly.
• फोन एकदम से बजा। = The phone suddenly rang.

In everyday speech, many speakers find एकदम से very natural for suddenly.
But एकदम by itself is also common and correct.

Other common choices:

• फोन अचानक बजा।
• फोन सहसा बजा। (more literary)

So the sentence is fine, but depending on region and style, a learner may hear एकदम से or अचानक more often.

Hindi word order is flexible, but not completely free. The most neutral order here is:

• फोन एकदम बजा।

This puts the subject first, then the adverb, then the verb.

You may also hear:

• एकदम फोन बजा।

This puts extra emphasis on suddenly. It can sound more dramatic or marked.

The most standard learning pattern is:

• Subject + adverb + verb

So this sentence is a good basic model.

Because Hindi often uses a simple past/perfective form by itself for completed events.

So:

• फोन बजा। = The phone rang.

You do not need था here.

If you add था, the sentence usually becomes less natural in this simple event-reporting context, unless there is some special narrative reason.

For a straightforward past event, बजा alone is normal.

It is a borrowed word from English phone, but it is fully normal in modern Hindi.

Hindi uses many loanwords, especially for modern objects. So फोन is completely natural.

You may also hear:

• टेलीफ़ोन = telephone
• मोबाइल = mobile phone
• फ़ोन with the dotted फ़ in careful spelling

In everyday writing, many people simply write फोन.

You know from the subject and the context.

With things like phones, bells, alarms, music, or instruments, बजना can mean different things:

• फोन बजा। = The phone rang.
• घंटी बजी। = The bell rang.
• संगीत बजा। = Music played.
• ढोल बजा। = The drum sounded.

So the meaning changes naturally with the noun.

Not usually. In this sentence, एकदम is more naturally understood as suddenly / all of a sudden, not loudly.

If you want loudly, you would normally use words like:

• ज़ोर से
• तेज़

Examples:

• फोन ज़ोर से बजा। = The phone rang loudly.
• फोन तेज़ बजा। = The phone rang loudly.

So एकदम is about the manner in the sense of suddenness or abruptness, not volume.

It is neutral and natural. It works well in everyday Hindi.

• फोन is everyday modern Hindi
• एकदम is common in speech
• बजा is standard

For a slightly more formal or written style, you might choose अचानक:

• फोन अचानक बजा।

But फोन एकदम बजा। is perfectly normal conversational Hindi.

Yes. This is a very useful pattern.

Examples:

• अलार्म एकदम बजा। = The alarm suddenly rang.
• घंटी एकदम बजी। = The bell suddenly rang.
• मोबाइल एकदम बजा। = The mobile suddenly rang.

Just remember that the verb form changes with the gender of the noun:

• masculine singular → बजा
• feminine singular → बजी

So:

• फोन बजा
• घंटी बजी