The oral surgeon had to give me laughing gas so that I would be relaxed enough for him to put the IV in for the anesthesia when I got my wisdom teeth out.
I had all four of my wisdom teeth out at once, while I was awake! It was pretty traumatising (but cheaper for my mom to pay the bill) without the gas & only just the local injections in my mouth. Then I drove myself ten miles home afterwards, half in shock (I was 19).
So I don't like going to the dentist, but I wouldn't say it's a phobia per se - because I know it's usually ok & not like that.
Unfortunately, I went back to that same dentist (wisdom teeth removal dentist) again when I was 40-something, visiting my mom near my hometown & I fractured my molar while I was there - it needed removing & a root canal. That was an awful experience too (and just the overall circumstances), but he was the only dentist who would see me as I'd been his patient 20+ years earlier.
Sure glad I never have to see that particular dentist again!