If your phone display says your phone is "Checking DNS", it is alerting you to the fact that it is not able to connect to the network. This may be because your internet is down -- and thus the device cannot communication with the DNS server.
Check to see if you are online on any other device. It may be neccessary for you to reboot your internet modem, and we also recommend rebooting the telephone.
Please reach out if rebooting the above devices does not resolve the issues.