मेरे भाई के पास मेरा फोन है।

Because भाई is followed by the postposition के पास, so भाई is in the oblique case.

In Hindi, possessive words like मेरा / मेरी / मेरे change form depending on:

• the gender and number of the noun, and
• whether that noun is in the direct or oblique case

Here:

• base form: मेरा भाई = my brother
• before a postposition: मेरे भाई के पास = with my brother / in my brother’s possession

So मेरे is used because भाई is masculine singular oblique here.

के पास literally means something like near, with, or in the possession of.

Hindi usually does not use a general verb exactly like English to have.
Instead, possession is often expressed with this pattern:

X के पास Y है
= X has Y
= literally, Y is with X

So:

मेरे भाई के पास मेरा फोन है।
literally: My phone is with my brother.
natural English: My brother has my phone.

Because मेरा agrees with फोन.

Here, फोन is treated as:

• masculine
• singular
• direct case

So the correct possessive form is मेरा.

Compare:

• मेरा फोन = my phone
• मेरी किताब = my book
• मेरे दोस्त = my friends / my friend in oblique

So even though the sentence already had मेरे earlier, that मेरे belongs with भाई, while मेरा belongs with फोन.

Because फोन is singular.

In this kind of possession sentence, the verb usually agrees with the thing being possessed, not with the possessor.

So:

• मेरे भाई के पास मेरा phone है। = My brother has my phone.
• मेरे भाई के पास मेरे फोन हैं। = My brother has my phones.

Since there is only one phone here, है is correct.

No. Here के is not a plural marker.

A very common beginner mistake is to think के must mean plural because of forms like लड़के. But in के पास, you should learn के पास as a set expression.

For possession, Hindi uses:

• मेरे पास = with me / I have
• उसके पास = with him/her / he/she has
• लड़की के पास = with the girl / the girl has
• लड़कों के पास = with the boys / the boys have

So के here is part of the structure X के पास.

Usually it means possession or control, not necessarily legal ownership.

So मेरे भाई के पास मेरा फोन है most naturally means:

• My brother has my phone
• My phone is with my brother

This often suggests a current situation:

• he is holding it
• he borrowed it
• he took it
• he has it with him

The ownership is actually shown by मेरा फोन = my phone.
The phrase मेरे भाई के पास only says who currently has it.

Yes, absolutely.

Both are correct:

• मेरे भाई के पास मेरा फोन है।
• मेरा फोन मेरे भाई के पास है।

The difference is mainly focus:

• मेरे भाई के पास मेरा फोन है focuses first on my brother
• मेरा फोन मेरे भाई के पास है focuses first on my phone

Hindi word order is more flexible than English, as long as the grammar is clear.

Because the plural oblique form would be different.

Here:

• singular direct: भाई
• singular oblique: भाई
• plural direct: भाई
• plural oblique: भाइयों

Since के पास requires the oblique, if you meant brothers, you would normally say:

मेरे भाइयों के पास मेरा फोन है।
= My brothers have my phone.

So मेरे भाई के पास means with my brother, singular.

Very simply:

Negative:
मेरे भाई के पास मेरा फोन नहीं है।
= My brother does not have my phone.

Yes/no question:
क्या मेरे भाई के पास मेरा फोन है?
= Does my brother have my phone?

This is a useful pattern to memorize:

• मेरे पास... है = I have...
• तुम्हारे पास... है = you have...
• उसके पास... है = he/she has...
• क्या ... के पास ... है? = Does ... have ...?