Origin of Hangul
Ledyard holds that the Koreans adopted five core consonant letters from ’Phags-pa, namely ㄱ "g" , ㄷ "d" , ㅂ "b" , ㅈ "j" , and ㄹ "l" . These were the consonants basic to Chinese phonology, rather than the graphically simplest letters (ㄱ "g" , ㄴ "n" , ㅁ "m" , and ㅅ "s" ) taken as the starting point by the "Haerye." A sixth letter, the null initial ㅇ, was invented by Sejong. The rest of the consonants were developed through featural derivation from these six, essentially as described in the "Haerye"; a resemblance to speech organs was an additional motivating factor in selecting the shapes of both the basic letters and their derivatives.
Gari Ledyard
Although several of the basic concepts of hangul came from Indic phonology through the Phagspa script, such as the relationships among the homorganic consonants and, of course, the alphabetic principle itself, Chinese phonology also played a major role. Besides the grouping of letters into syllables, along the lines of Chinese characters, it was Chinese phonology, not Indic, that determined which five consonants were basic, and therefore to be retained from Phagspa. These were the tenuis (non-voiced, non-aspirated) plosives, "g" for ㄱ , "d" for ㄷ , and "b" for ㅂ , which were basic to Chinese theory, but which were voiced in the Indic languages and not considered basic; as well as the sibilant "s" for ㅈ and the liquid "l" for ㄹ . (Korean ㅈ was pronounced in the 15th century.)