First, check if GPS access is enabled in phone settings. If it is enabled, but you still do not get GPS signal, check if other apps on the phone see GPS. For example, you can use this test app on Android phone: GPS Status. If other apps don't have GPS access either while you are outdoors with a clear view of the sky, you may want to check with your phone manufacturer support. There may be a hardware or system problem.
If you experience GPS problems in other apps (Apple Maps, Google Maps), there may be the hardware issue described here - https://discussions.apple.com/thread/7248028?start=0&tstart=0
Temporary workaround is to turn off bluetooth.
Permanent solution is to change the antenna cable.