Dear friend, We sincerely apologize for the unsatisfactory experience with the product when using it on a phone case. Yes, The sublimation paper can be used on both textiles and items like phone cases and aluminum, and phone cases and aluminum require a coating. Please check if yours has a coating. To ensure you use it correctly, here are the product's transfer times and temperatures: A: Transfer time and temperature for aluminum plate: 180°C-200°C, 25 seconds B: Transfer time and temperature for phone case: 1. Using a 3D vacuum machine: 130°C-150°C (film) 2. Using a 3D vacuum machine: 1240°C-350°C (3D hard case) Please record a video of the entire process during testing and send it to us. Our technical team will verify the operation is correct. Thanks you for your cooperate !