てもいいですか　vs. causative verb + もらってもいいですか


> 電話を **使わせて** もらってもいいですか。

I know that _causative verb form + てもらう_ means to let somebody do something.
And てもいいですか is for asking for permission. But I don't quite understand the use
of these 2 constructions together.

If I wanted to ask someone to let me use their phone, I would possibly say:

> 電話を使ってもいいですか。

How are the meanings of the two sentences different? Is "電話を使わせてもらってもいいですか"
just more polite?




てもいいです - May I do(To Grant Permission)

causative form + もらってもいいです - Would you Please let me do(To seek permission)




> 電話を使ってもいいですか。

literally means

> Is it ok for me to use the phone?

And

> 電話を使わせて貰ってもいいですか。

literally means

> Is it ok for me to be let to use the phone by you?

The latter one sounds more polite.

