if a phoneme appears twice in a english word, it will be pronounced as the same allophone both times; ie, two different phoneme of two different allophones of the same phoneme cannot be used in a single word.
is this right?
If a phoneme appears twice in a word, it will be pronounced the same if and only if the tokens of the phonemes appear in the same context (as defined by the allophonic rule). The phoneme /t/ is aspirated foot-initially, and it is glottalized syllable-finally after a vocoid: "tout" is pronounced [tʰæʊt˺]. It is non-aspirated and non-glottalized elsewhere, as in "stacked" [stækt], or "statistician" [stæ̀ɾəstɪ́ʃn̩] (where two of the t's are in the same environment and have the same allophone, and the third on in the middle is in a different context as has the allophone appropriate for foot-medial intervocalic position).