What is T19, under Bluetooth, other devices on Iphone?

We wouldn't know. Your iPhone is clearly seeing a Bluetooth device, which is named T19. It doesn't have to be your device, nor would it necessarily mean you can connect to it. Your phone just sees that device broadcasting a Bluetooth signal.

It would be better if you can please post a screenshot, in order to understand the phenomenon better.

You may get better and prompt responses if you may kindly provide the iPhone Model that you have and the iOS version if it is known to you.