It should work with any type of phone, provided that the device is provisioned properly and the device id is obtained and the device is online. The API document also mentioned the reason (since device IDs for WebRTC/Mobile apps cannot be obtained).

I can retrieve the device id( which is online), but when trying to make the supervise party api call. I get 
 

curl --request POST \
  --url 'https://platform.ringcentral.com/restapi/v1.0/account/~/telephony/sessions/telephony-session-id/parties/party-id/supervise' \
  --header 'accept: application/json' \
  --header 'authorization: Bearer ****' \
  --header 'content-type: application/json' \
  --data '{"mode":"Listen","supervisorDeviceId":"801539065035","agentExtensionId":"919349035","autoAnswer":true,"mediaSDP":"sendOnly"}'

{
  "errors": :
    {
      "errorCode": "TAS-119",
      "message": "Can't reach deviceId specified in request"
    }
  ]
}

Can you make a normal phone call to that device?

Looks like this was because the phone would not send a OK response when supervised. Is not observed once that happens.