Database
db={"users":[{user_id:"1234",phone_number:"+9600000000000"}],"users_info":[{name:"John Smith",phone_number:"+9600000000000",age:"45",address:"DC"}]}
Query
db.users.aggregate([{"$match":{"phone_number":"+9600000000000"}},{"$lookup":{"from":"users_info","localField":"phone_number","foreignField":"phone_number","as":"user_info","pipeline":[{"$project":{"_id":0}}]}},{"$replaceWith":{"$mergeObjects":["$$ROOT",{"$first":"$user_info"}]}},{"$project":{"_id":0,"user_info":0}}])