Apex domains cannot have CNAME records.
Question and response
Question
dig tel. NS
Answer
tel. 5 NS anycast23.irondns.net.
tel. 5 NS anycast24.irondns.net.
tel. 5 NS anycast9.irondns.net.
tel. 5 NS anycast10.irondns.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0