Apex domains cannot have CNAME records.
Question and response
Question
dig rocketpbx.com. NS
Answer
rocketpbx.com. 1 NS dns1.rocketinternet.net.
rocketpbx.com. 1 NS dns2.rocketinternet.net.
Authority
The response has no authority records.
Additional
dns1.rocketinternet.net. 1 A 66.159.51.114
dns2.rocketinternet.net. 1 A 66.159.51.115
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0