Tautosyllabicity
Two or more segments are tautosyllabic if they occur in the same syllable. For instance, the English word "cat" is monosyllabic and so its three phonemes, and are tautosyllabic. They can also be described as sharing a 'tautosyllabic distribution'.
Phonemes that are not tautosyllabic are heterosyllabic. For example, in the English word "mustard", and are heterosyllabic since they are members of different syllables.