Why are h’s added in Thai words like “Thailand” “Phuket” and “Ayuthaya” when the h’s actually make the words appear to be read differently? The only thing I can think of is that the words come from French, but even in French “ph” is pronounced like “f.”
Many languages make a distinction between aspirated and unaspirated stops. In English, the “p” in “pot” comes with a free little puff of air (aspiration) that you can feel if you hold your finger in front of your lips as you speak. Again in English, the “p” in “spot” is unaspirated — no puff. These have complementary distribution in English, so native speakers usually hear them both as the same sound.
However, in romanization of languages where it makes a difference, ph = aspirated p, and p = unaspirated p.
I don’t speak Thai, though, so if someone wants to come along and tell me I’m full of bhullsit, welcome.
I love it when you all talk phonemes.
Great, now I’m saying “po!-nemes”.
It’s quite simple really. The H after the T indicates the T is pronounced AS a T. Thai has extra consonants, extra sounds, that we don’t have in English. There’s one sound that is halfway between a D and a T; I cannot make it, but pronouncing it like a D is MUCH closer than pronouncing it like a T. For instance, the northern province of Tak. The A is like the A in “father,” so Tak sounds very much like the English word “doc” (except in this case, the vowel is much more drawn out: “do-o-o-ck”). (Many non-Thai speakers pronounce it like the English word “tack,” which is flat wrong.)
Similarly, the H after the P means the P is pronounced as a P. There is a sound that is between a B and a P, and no H is that sound, but you are more correct to pronounce it like a B than a P. For instance, the town of Pai in Mae Hong Son province is pronounced more like the English word “bye” than “pie.” But many farangs (Westerners) have set up businesses in the area with names like Pai in the Sky (it’s in a mountainous area) and such, trying to make a pun out of the English word “pie” but not realising it is NOT pronounced like “pie.”
There is a lot of inconsistency in transliteration. The H is often not transliterated over. But there are actual consonant symbols for all of these sounds in the Thai alphabet, so if you can read Thai, like I can, then you can see what the correct sound should be.
They have these in Vietnamese too. I can’t make it either, but the closest I can come is trying to say an English T sound without exhaling so much (like we do when making a D sound). It does sound more like a D.
Mmmm… Pho.
Great. Now i’ll be reading that in a Weebl and Bob voice.
“Mmmm… pho. Pho pho pho pho pho. Pho. Mmmm pho.”
When come back, bring pho?
What, you mean “Phuket” isn’t actually pronounced “f*** it”?
*runs off to clear things up with the travel agent"
There’s a story, possibly apocryphal, about a Thai restaurant in New York called Phuket being refused a license by the city, because of the perceived incorrect pronunciation of the name. 
(And note the absence of an H after the K. That means the K is pronounced like a G.)
Yes, I’ve noticed this on menus. I know nothing of Thai, except recognizing a few menu items. “Chicken” gets transliterated as “gai,” “kai,” or even “khai,” depending on where you go. “Fried” is “pad” or “pud.” Rice is “gao,” “kao,” or “khao.” I’ve seen Thai holy basil as “ga-prao,” “gaprao,” “gaprow,” “kaprow,” even “krapow.” It seems Thai transliterations are all over the place.
What’s the closest Anglicization of my favorite Thai dish, gai pad gaprao (Thai holy/hot basil chicken)?
“Chicken” should never be transliterated as khai, because that means “egg.”
The dish you mention I routinely transliterate as phat kraphao kai.
Wait…soooo…that means that Phuket is actually pronounced like Puget? As in Puget Sound? Buuut…not.
d&r
Wow. The transliterations really are variable. How the heck is it that the consonants gets thrown around all over the place? I thought almost surely “gaprow” or “kaprow” was the right word for the Thai hot basil, based on how much more often I’ve seen it, but the correct consonant order is the “r” in the first syllable, not the second. Why is this so confusing? Are there dialects that say “gaprow” and others “grapow”? I mean, I can see "k"s for "g"s and other sort of voiced/unvoiced transpositions, but completely altering the order of the consonants…weird.
A G, not a J. 
Thai has a definite R sound and a letter R. It is in the first syllable, not the second: kraphao. There’s a lot of confusion in transliterations. You get used to it. Even with family surnames, it’s very common for each member of a family to spell their surname differently in the Roman alphabet. In Thai, it’s all spelled the same of course.
You should see a lot of the English-language menus over here. “Fried crap” (crab) is a standard.
In almost all transliterations, you never see a G at the beginning of a syllable, and I mean never. There is a G sound and a letter G, but it’s rendered as K in our alphabet. The K sound is rendered Kh. You only ever see the G written at the end of -ing spellings .
I neglected to answer this. No, it’s not a dialect thing. No Thai would ever say kaphrao. In that Thai word, the R is always in the first consonant. But in trying to write Thai myself, I can see how that happens. For me, reading Thai is much easier than writing; my letters go all over the place, too.
Funny thing is sometimes a letter gets added in transliteration that simply does not appear in the original word. The example I can think of off the top of my head comes from Laos. The old royal capital of Luang Prabang has no R in the written Lao version! Thais and Lao call it Luang Phabang (it’s a P sound despite no H in the transliteration). I have no idea how the R got into the romanized version, but it’s standard now.