Apex domains cannot have CNAME records.
Question and response
Question
dig us-dcc-phoenix-2.ocs.oraclecloud17.com. NS
Answer
us-dcc-phoenix-2.ocs.oraclecloud17.com. 5 NS ns3.p200.dns.us-dcc-phoenix-2.oci.oraclerealm17.com.
us-dcc-phoenix-2.ocs.oraclecloud17.com. 5 NS ns4.p200.dns.us-dcc-phoenix-2.oci.oraclerealm17.com.
us-dcc-phoenix-2.ocs.oraclecloud17.com. 5 NS ns1.p200.dns.us-dcc-phoenix-2.oci.oraclerealm17.com.
us-dcc-phoenix-2.ocs.oraclecloud17.com. 5 NS ns2.p200.dns.us-dcc-phoenix-2.oci.oraclerealm17.com.
us-dcc-phoenix-2.ocs.oraclecloud17.com. 5 NS ns7.p200.dns.us-dcc-phoenix-2.oci.oraclerealm17.com.
us-dcc-phoenix-2.ocs.oraclecloud17.com. 5 NS ns6.p200.dns.us-dcc-phoenix-2.oci.oraclerealm17.com.
us-dcc-phoenix-2.ocs.oraclecloud17.com. 5 NS ns5.p200.dns.us-dcc-phoenix-2.oci.oraclerealm17.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0