उसका फोन मेरे पास है।

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Breakdown of उसका फोन मेरे पास है।

• होना: to be
• फोन: phone
• के पास: to have

Questions & Answers about उसका फोन मेरे पास है।

What does उसका mean here?

उसका means his, her, or sometimes its.

Hindi does not mark natural gender in this possessive form the way English does, so उसका फोन can mean:

• his phone
• her phone

You usually understand which one from context.

Why is it उसका and not उसकी or उसके?

Because Hindi possessives agree with the thing being possessed, not with the owner.

Here, the possessed noun is फोन, which is treated as masculine singular in Hindi. So the correct form is:

• उसका फोन = his/her phone

Compare:

• उसकी किताब = his/her book
  because किताब is feminine
• उसके जूते = his/her shoes
  because जूते is masculine plural

So उसका is chosen because फोन is masculine singular.

Why is it मेरे पास and not मैं पास or मेरा पास?

Because पास is used like a postposition here, and pronouns change form before postpositions.

The pronoun मैं becomes मेरे before a postposition: