The principles of phonological analysis can be applied independently of modality because they are designed to serve as general analytical tools, not language-specific ones. The same principles have been applied to the analysis of sign languages (see Phonemes in sign languages), even though the sub-lexical units are not instantiated as speech sounds.
If it is possible to answer this question, answer it for me (else, reply "unanswerable"): What other types of language have the speech sound principles been applied to
unanswerable