All transliterations of Thai names or words are nothing more than imperfect approximations of how they should be pronounced. The definitive spelling is the one in Thai characters. As others have said, the "h" after a consonant only indicates that the consonant should be aspirated. T-ai, not D(t)-ai, P-ooket, not B(p)-ooket. In no case does the "h" combine with the consonant to form English-style "th, " or "ph" sounds.