Getting the queried result in the form of json structure

I am using postgresql for my webapplication. I am new to this
Postgresql-json. I Just want to get the select query result in the form of
json structure.
Here are my details:

Create table
============
- create table sample(id, serial, info jsonb);
Insert query
============
- insert into sample("info") values('{"person": {"phone":
9804484234,"name":{"firstname":"Alice", "lastname":"bob"}, "empId": "E067",
"age":25}');

select query:
=============
select "info"->'person'->>'lastname' from sample;

result: bob

but I want to get the above result along with the json nodes like below:

result: {"person":
{"name":
{"lastname":"bob"}
}
}

could any tell me how to get my expected result structure from database.

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