Google's Better Together pairing of Chromebooks and Android phones allows Pixel and Nexus users to automatically share a data connection from their phone to Chromebook. Now, however, a wider choice of devices is offered compatibility.
Due to limited availability, you have been denied access to the Instant Tethering feature. In short, an Android device can automatically connect to a Chromebook if the book does not detect a usable Wi-Fi connection.
As mentioned before, this is part of Google's "Better Together" feature. In Chrome OS, this is an attempt to create a combination of laptop and phone that looks like the Mac. Once connected, users can send Smart Lock, Instant Tethering, and even text messages from their Chromebook. The thing is, it was only compatible with Google phones (Nexus, Pixel). Until now.
Of course, availability is still pretty limited. It is only available in the Chrome OS Developer Channel and . You need a compatible phone. Small steps. However, before we look at how to do it, there are a few things to keep in mind:
- You still need a compatible tethering plan. If you have no connection to your mobile plan, it will not work. Google is not interested in helping you fool the forwarders. Excuse me.
- Your phone must be compatible. Before you complete the steps to set up your Chromebook, go to Settings> Google and search for "Instant Tethering" on your phone. If this is not the case, it will not work.
Let's do that.
: Connect your Android phone
If you're on the Developer Channel, go ahead and jump to your Chromebook's Settings menu. From there, scroll to "Connected devices" and click the "Setup" button.
menu item In this new menu, click the drop-down list on the left and select your option Phone. Then click on the Accept & Continue button.
You must enter your password to continue, but then you can proceed. The connection should be made pretty soon.
The Connected Devices menu item displays all available options: Smart Lock, Instant Tethering, and Messages. If Instant Tethering does not appear for you continue to the next step. If is displayed, you can jump to step 3.
Menu Step 2: Enable the Instant Tethering Flag  If Instant Tethering is not displayed as an option, you must enable it in the Chrome OS Flags menu. Open a new browser tab and enter:
chrome: // flags / # instant-tethering
Select "Enabled" from the drop-down menu.
Then click on the click on the restart button below.
Step 3: Enable Instant Tethering on Your Phone
Finally, you need to get Instant Tethering running on your phone. First, open the settings menu and then scroll down to Google.
Search for Instant Tethering in the Google menu. 
Tap this menu and enable the "Make Data Connection" option.
The system may automatically notify you to enable this option when the Wi-Fi connection is disconnected. However, you can preventively activate this to be one step ahead.
This should allow your phone to automatically provision a data connection to your Chromebook when it's not connected to a previously-used Wi-Fi connection. However, it seems to be a slow rollout and is not yet available on all Android phones. I've received reports that users are working on Samsung, Nokia and OnePlus devices, even though they are not yet available on my OnePlus 6T, so your mileage may vary.
on Android Police, About Chromebooks