In cream /kriːm/, the /k/ is typically aspirated [kʰ] because it occurs at the start of a stressed syllable.
➡ In scream /skriːm/, the /k/ is typically unaspirated [k] because it follows /s/.
➡ Even though they sound slightly different (aspirated vs unaspirated), they are variations of the same phoneme /k/ in different phonetic contexts.
they are allophones: context-dependent variations of the same phoneme /k/ that do not change meaning.
