Hi there, dealing with the issue that the SD card is not detected by your phone and PC, I suggest you check the connection first.
For checking the connection, you can insert the SD card into any other devices to see if it can be detected. Or, you're suggested to utilize a new SD card adapter or SD card reader to reconnect your memory card and the phone/PC. If you ensure that the connections go well, then it indicates that your SD card is problematic.
Since the SD card is not detected by any device, it's impossible for the device to recognize or mount it. Hence, you have no access to it.
For your long-range storage requirement, you'd better purchase a new and high-quality SD card. Meanwhile, always backing up your SD card is indispensable in case that you suffer from data loss.