That s not true An allophone can only use phonetic information not morphological part of speech information What you are describing is morphophonological alternation The definition of phoneme is the smallest segmental unit of sound employed to form meaningful contrasts between utterances That means that if the alternation between d and t indicates whether a word is a noun or a verb then the difference between t and d indicates meaning so it is phonemic I can explain this further or give you more evidence but I will just tell you that you are misusing the words phoneme and allophone