ok so ive been licensed about 4 months and still feel kind of awkward on voice. my question is like... do you always have to use the NATO phonetics or is it just when things are unclear? i was on a local repeater the other day and someone just said their callsign normally without spelling it out phonetically and it was totally fine, but then on HF everyone seems to go full NATO every single time even when conditions are good. is there a rule about this or is it just one of those unwritten things

also side question, does it matter if i use a slightly different word? like i know some people say "Sugar" instead of "Sierra" or whatever. is that going to bother people

No hard rule that says you must use phonetics every single time — it's really just about whether the other station can copy you clearly. On a local repeater with good signals and no QRM you can just say your call and everyone hears it fine. But on HF especially when the band is noisy or you're working DX, phonetics are just how you make sure the other op actually gets your call right. Nothing worse than getting into a log wrong because someone heard B instead of D or whatever.

As for mixing in non-standard words, yeah some old timers do it and it's not the end of the world, but honestly stick with NATO when you can. The whole point is that those specific words were chosen to be distinct from each other even through static and accents. "Sugar" and "Sierra" both start with S so it's fine, but some substitutions can actually cause more confusion than they solve. Just learn the standard ones, after a while you say them without even thinking about it.

honestly the repeater vs hf thing took me a while to get too. i still sometimes forget to go phonetic when i first key up on 40m and then have to repeat myself anyway lol so now i just default to phonetics whenever im giving my call to someone new even on the repeater, easier than trying to judge the conditions every time

the non-standard words thing -- ive heard people use all kinds of variations, some old guy on the local net always says "Mexico" for M instead of "Mike" and nobody seems to care but i do notice that when i was trying to work a station in Japan once he clearly didnt recognize one of my phonetics and I had to repeat it. so thats kind of an argument for sticking to the standard ones i guess