Apex domains cannot have CNAME records.
Question and response
Question
dig ext.philips.com. NS
Answer
ext.philips.com. 5 NS ns2.ext.philips.com.
ext.philips.com. 5 NS ns3.ext.philips.com.
ext.philips.com. 5 NS ns1.ext.philips.com.
Authority
The response has no authority records.
Additional
ns1.ext.philips.com. 5 A 57.67.40.20
ns2.ext.philips.com. 5 A 57.77.21.76
ns3.ext.philips.com. 5 A 57.73.36.68
ns1.ext.philips.com. 5 AAAA 2a01:ce89:8001:0:57:67:40:20
ns2.ext.philips.com. 5 AAAA 2a01:ce95:4001:100:57:77:21:76
ns3.ext.philips.com. 5 AAAA 2a01:ce9d:1:0:57:73:36:68
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0