You are mixing up different levels of language. Here is map:
sounds -> phonemes -> morphology -> syntax -> semantics -> pragmatics
glyphs -> characters -/
A phoneme is a unit of spoken language. It is a recognisable sound. So in English, there are sounds /r/ and /l/ These are recognised as different by English speakers. In written English, the equivalent is the "letter".
At the next level, phonemes are combined to make morphemes and an affix is a type of morpheme. Examples are "un-" or "-ing". It is possible for a morpheme to have just one phoneme (or just one character in written English). For example in British English the morpheme "-er" is (often) a single phoneme /ə/ and the prefix "a-" is a single letter.
So an affix may be formed from a single phoneme. But you are mixing different levels of language and can become confused.
In the case of "-oh" It is actually two phonemes /əʊ/. It isn't a common suffix in English. There is a suffix "-o" which forms colloquial forms, like "kiddo". But not "thato" or "gameo".
Sounds are sounds. Sounds as recognised by speakers of a language are phonemes. For example [r] and [l] have different sounds, and are different phonemes in English. But in Japanese they are the same phoneme. Japanese speakers literally can't hear a difference between fly and fry or right and light. And phonemes aren't morphemes. Morphemes are elements that can be combined to make a word. "-ing" is a morpheme so is "un-" and so is "cat". When you combine one or more morphemes to make a word, and then one or more words to make a sentence: then you have "meaning". And if you interpret that sentence in context, you have understanding!