Xda-Developers | Chrome OS 73 brings Instant Tethering to non-Pixel smartphones

In addition to making it possible to add user-designated top-level folders in My Files, Chrome OS 73 adds the ability to instantly tether your Chromebook to your Android phone, even if it's not from the Google's Pixel line. As reported on the Keith I Myers blog, Instant Tethering can be activated with non-Google phones, such as Samsung's Galaxy Note 9. There are some caveats though:

Your carrier must allow tethering, which might cost extra depending on your plan.
Not all device-carrier combinations support Instant Tethering. For example, I was unable to get this feature to work on my OnePlus 5T on Google Fi (had I been on some other carrier I suspect my 5T would have worked though). I should point out that I was easily able to use Instant Tethering with my Pixel 2 XL on Fi.
Your phone should have the following minimum requirements: Android 7.1 or higher, and Google Play Services 14.9.99.
Currently, Chrome OS 73 is only available in the Canary and Dev channels, but it should soon migrate to the Beta and Stable channels.

In order to activate Instant Tethering to your non-Pixel phone, do the following:

Copy and paste the following URL in your browser in order to enable the Instant Tethering flag: chrome://flags/#instant-tethering
Once you have enabled the flag, go to Connected Devices in your Chrome OS device's settings and set up your phone.
Turn off WiFi on your Chrome OS device and you should be prompted to connect to your phone. If your particular combination of device and carrier plan are supported, you'll see your device name instead of the "Pixel 2 XL" in a notification as depicted below.
Once connected you'll be able to see your phone's battery level in the networking section in your Chrome OS notification panel so you can get an idea of how long your Internet connection will last before you have to connect your phone to a charger.