Try taking it out and restarting your phone and then put the SD card back in and see what it says. I assume that it doesn't read the card after the message? If still the same thing put it in another device and see if it can read the card. If yes and your phone still cannot it is your phone then. If the restart doesn't do it I'd do a factory reset first after backing up everything. If that doesn't do it and your phone is up to date then I'd invoke the warranty.
A lot of the inexpensive off-brand SD cards sold on internet sites are not honestly represented. Some have their boot data trafficked so that they read out as having a lot more than their actual physical capacity. They may work for a while and then... kaboom, the honeymoon is over. You may get intermittent reads or nothing at all, across all platforms. If you have an adapter, try the card in a PC or Mac.
There are SD card tester apps available on Google Play.