shanai de naisen o tsukaimasu.

I use the internal extension inside the company.

Breakdown of shanai de naisen o tsukaimasu.

• を: direct object particle
• で: location particle
• 使つかう: to use
• 内線ないせん: an internal phone extension

Questions & Answers about shanai de naisen o tsukaimasu.

How do you read 社内, 内線, and 使います?

They are read as:

• 社内 → しゃない
• 内線 → ないせん
• 使います → つかいます

So the whole sentence is read:

しゃない で ないせん を つかいます。

What does 社内 mean exactly?

社内 literally means inside the company or within the company.

It can refer to:

• the company building or office space
• the company as an internal organization

So it often has the nuance of internally, not just at the company in a broad sense.

Why is で used after 社内?

で marks the place where an action happens.

In this sentence, the action is 使います (use), and 社内で shows the location or setting where that action takes place.

So:

• 社内で = in the company / within the company
• 内線を使います = use the extension line

A good way to think of で here is: this is where the action happens.