Try this first.
Disconnect all of the cameras from the back of the NVR
Use a paperclip to push and hold the reset pinhole for 30 seconds
Wait 2 min for the NVR to come back up
Reconnect cameras to the back of the NVR
Check if cameras show on the monitor connected to the NVR
If yes, check the phone access
If no, check the NVR’s network settings, and post a picture here.