I tried putting the code as mentioned in the documentation and I received an error.
vultr-cli instance create --region ewr --plan vc2-1c-1gb --os 148 --label my-instance --ipv6 false
error creating instance : {"error":"Cannot add instance. Specified os_id not available","status":400}
Vultr documentation does contain OS ID's, but it also warns:
Run
oslist
from the CLI and select an ID from the response. Here is a link to the documentation for the CLI if you need help running the oslist command.