In Latin spelling, individual letters mostly corresponded to individual phonemes, with three main exceptions:

Phonemic awareness is the ability to hear and manipulate individual phonemes.

This might mean that children are aware of syllables as units of speech early on, while they don't show awareness of individual phonemes until school age.

The purpose of the experiment was to give a reason to why in background of extraneous sounds, masked individual phonemes were still comprehensible.

The analysis indicates the problems LA must cope with even when a large percentage of the individual phonemes have been correctly identified.

Furthermore individual phonemes may also be stressed.

Distinctive feature phonologists have also claimed that when children are learning their first language, they acquire features rather than individual phonemes.

They are regarded as syllable features for several reasons, but most importantly because they cause contrast between syllables rather than between individual phonemes.

There are 10 vowels in Czech which are regarded as individual phonemes.

It requires that a voice actor record each individual phoneme, the smallest unit of audible speech.