Well, the point of SMS is as a backup to the 2FA system. It's primarily used in situations like getting a new phone and forgetting to write down the serial number and restore code. You can fall back to getting a token via SMS to prevent yourself from getting locked out of your account and needing to jump through hoops with support to get access again. It's not really meant as an additional security step. As such, using the same device should be fine for that.