A sender in the communication process has very good grammar. This competence is basically

A sender with very good grammar shows syntactic competence.

Syntax is the arrangement of words into correct sentence structure, which grammar governs.

Phonemic competence is mastery of speech sounds, not sentence rules.

Semantic competence is command of meaning, a different layer from grammar.

Pragmatic competence is fitting language to social context, not grammatical form.

Good grammar is the structural correctness that syntax measures.