My sd card is 128gb. After I inserted it in my phone and transferred all the necessary data, 125gb remained. However, when I try to download or upgrade, I get a message saying 'insufficient storage space'. If I still have 125gb remaining, why does my phone not recognize this?
Your phone's default download location is the internal storage, not your SD card. SD cards can be used to store pictures/videos/media, but apps and software upgrades have to use your phone's internal storage.