How much of a functional load must a phone carry to be considered its own phoneme?
For example, my idiolect of English has a marginally distinctive glottal stop. However, it exists distinctively in only two words I can think of, both interjections:
/ʔju/ [ʔjɨw] eew, distinct from
/ju/ [jɨw] you/yew/ewe and
/hju/ [hj̊ɨw] hue/hew; and
/ˌɐˈʔɐ/ [ˌʔɐˈʔɐ] uh-uh, distinct from /ˌɐˈhɐ/ [ˌʔɐˈhɐ] uh-huh.
(This is independent of the common utterance-initial glottal stop insertion before vowels, and /ʔ/ as an allophone of /t/ in British English.) Is two minimal pairs enough to establish a phoneme?