so ive been licensed for a few months now and i keep hearing people on the local repeater just say their callsign normally like just the letters and numbers without doing the whole alpha bravo charlie thing and then other times people go full NATO phonetics every single time. i did my tech exam and learned the phonetic alphabet but honestly i wasnt sure if theres like a rule about when you have to use it vs when its optional. is it just a courtesy thing or is there actually a requirement somewhere in part 97 or whatever. i dont want to sound like an idiot either way

No hard rule in part 97 that says you must use phonetics every time, its more of a best practice thing especially when conditions are rough or theres QRM. On a clear local repeater most people just say their call straight because everyone can hear fine. Where it really matters is on HF when youre working someone whos struggling to copy you or during a net check-in where the net control is writing down a lot of calls fast. honestly just use your judgement, if somone asks you to say it again go ahead and spell it out phonetically. most elmers will tell you to use phonetics more rather than less when youre starting out just so you get comfortable with them

yeah what he said, and also worth knowing some people make up their own phonetics which is technically fine but can confuse people lol. heard a guy once use "Wisconsin" for W and it just threw me off for a second. stick with NATO and youll be understood everywhere, even by foreign stations which is kind of the whole point of standardizing it in the first place