Make sure that the phone is assigned to a user. You can do this by logging into Ooma Office Manager and following the steps under Through the Devices Menu in this knowledgebase article that discusses assigning a device to a user.

If the device is already assigned to a user, restart the phone. You can do this by disconnecting the device’s power, waiting for 30 seconds, and then plugging the power back in.

Note: If you are still having issues with getting your phone working, please call customer support. Do not do a factory reset of the phone.