"No amateur station shall transmit... obscene or indecent words or language..."
Saying the original phrase Let's Go Brandon was derived from would certainly violate this, but would saying Let's Go Brandon be an issue?
As a comment by user sonyfreak points out, quoting the Wikipedia article "Let's Go Brandon":
"Let's Go Brandon" is a political slogan and Internet meme that has been used as a minced oath for "Fuck Joe Biden", in reference to Joe Biden, the 46th president of the United States.
According to the official FCC page "Obscene, Indecent and Profane Broadcasts":
Indecent content portrays sexual or excretory organs or activities in a way that is patently offensive but does not meet the three-prong test for obscenity.
This page does not cite any laws or sources. The "three-prong test" would ber the rule from Miller v. California, 413 U.S. 15 (1973)
A minced oath such as "Let's Go Brandon" would not appear to violate this rule.
Violations of the rule against indecent content that the FCC may penalize are known as "Actionable indecency". These rules originated in the case Federal Communications Commission v. Pacifica Foundation, 438 U.S. 726 (1978) but have since been modified by the FCC.
Such violations may be penalized under 47 USC 502 or 47 USC 503
Lili Levy, in The FCC's Regulation of Indecency (April 2008) has argued that these modified rules may not be constitutional as applied.
47 USC 152 defiens the scope of this chapter as:
The provisions of this chapter shall apply to all interstate and foreign communication by wire or radio and all interstate and foreign transmission of energy by radio, which originates and/or is received within the United States, and to all persons engaged within the United States in such communication or such transmission of energy by radio, and to the licensing and regulating of all radio stations as hereinafter provided; but it shall not apply to persons engaged in wire or radio communication or transmission in the Canal Zone ...
47 USC 153 the definitions section of this law) specifies that:
The term “amateur station” means a radio station operated by a duly authorized person interested in radio technique solely with a personal aim and without pecuniary interest.
...
The term “broadcast station”, “broadcasting station”, or “radio broadcast station” means a radio station equipped to engage in broadcasting as herein defined.
...
The term “broadcasting” means the dissemination of radio communications intended to be received by the public, directly or by the intermediary of relay stations.