This article explains how to get voice chat on Roblox. The instructions are valid for all platforms.

Regardless of which platform you choose to play on, you will need to use your smartphone to verify your age before you can enable chat. You will need to provide a government-issued ID (such as a passport or driver's license) that proves you are at least 13 years old.

Here's how to get Roblox voice chat:

On the Roblox website, select the Settings gear and choose Settings.