Is the other phone a LG as well? The reason I ask is formatting. Some devices will format a card so that it cannot be read by another device. Especially if the card was used in a phone running Marshmallow and the card was set as Internal rather than External.
If you are wanting to use it in the new device, and use the information on it in the new device, you are probably going to have to remove the stuff off the card, to say a computer, then put the card in the new device. Next format it in the device and move the stuff back to the card/device from the computer.
This would work if you no longer plan on using the other phone. However if you do plan on using it, then this would not work as it could make the card unreadable by the prior...