When a noun is modified by an adjective, and when it is clear what you are referring to, you can use the particle の(no) to replace the thing to avoid repetition.

In this case, の is used like "one" in English.

わたし　は　しろい　iPhone　を　もっています。すずきさん　は　くろい　の　を　もっています。

I have a white iPhone. Mr. Suzuki has a black one.

* In the second sentence, iPhone is replaced with の since it is clear that I am talking about iPhone.

この　ラーメン　おいしい　です　ね。

This ramen noodle is tasty, isn't it?

はい、でも　わたし　は　もうすこし　からい　の　が　すき　です。

Yes, but I like a bit more spicy one better.

* ラーメン is replaced with の

おかし　が　たくさん　あります。すきな　の　を　もって　いって　ください。

There are lots of snacks. Please take the one you like.

* おかし is replaced with の

これは　さとうさん　の　とけい　です　か。

Is this Mr. Sato's watch?

はい、それ　は　さとうさん　の　です。

Yes, it is Mr. Sato's.

* You can also use  の to show the thing is owned by a person such as "mine" or "yours"

* In this case, の is used to show the watch is owned by Mr. Sato.

References: 

Noun A "no" Noun B

https://anchor.fm/yuya-sato/episodes/Noun-A-no-Noun-B-emo577

Sentence-ending particle "ne" and "yo"

https://anchor.fm/yuya-sato/episodes/Sentence-ending-particle-ne-and-yo-emureo

Adjectives

https://anchor.fm/yuya-sato/episodes/Adjectives-en9o8v

The Purpose of Movement + go

https://anchor.fm/yuya-sato/episodes/The-Purpose-of-Movement--go-eno23j

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