Slow Time

The clock on my phone is slow for some reason. Slow, as in I can set it to the correct time either by rebooting the phone or unchecking and rechecking the box next to Automatic date & time in my Date & time settings, and as time goes on, the phone will lag behind. If I compare the time on my phone to the time on another device like my computer a while later, it will be a few minutes behind. What's going on?