Phonemics is the study of the phonemes of a language — which sound-pieces a language uses, and which differences count as different words. It is a subject-name, like physics, built with -ics. Though actually, many linguists now prefer the broader word phonology, which also covers how sounds pattern in syllables and across words. You will still meet phonemics in older books and in some American classroom lists. It is academic language, not a word for everyday fear or telephones.