The spelling of the phrase "most good sized" can be explained with the use of IPA phonetic transcription. The word "most" is pronounced /məʊst/, where the "o" makes the /əʊ/ sound. The word "good" is pronounced /ɡʊd/, with the "oo" making the /ʊ/ sound. Lastly, the word "sized" is pronounced /saɪzd/, where the "ize" makes the /aɪz/ sound. Therefore, the correct spelling of this phrase is "most good sized." It means something is bigger than good in size.