Definition of "phonological"

[...] Phonological competence is also reflected in intuitions about phonological structure: any English speaker intuitively feels, for example, that the sequence 'black bird' can either be a single phonological word (BLACKbird, with primary stress on black = a species of bird, like thrush, robin, etc.), or two independent phonological words (BLACK BIRD or black BIRD = bird which is black, as opposed to 'white bird', 'yellow bird', etc.).

1988, Andrew Radford, Transformational Grammar, Cambridge: University Press, page 5

Each language has its own distinct phonological qualities which a counter can tap into with effect. It is not necessarily specific phonemes (though these can sometimes be diagnostic), but rather the frequency and phonotactic distribution of each disparate set of phonemes that go together in the speech stream in certain recognisable ways.

2019, Li Huang, James Lambert, “Another Arrow for the Quiver: A New Methodology for Multilingual Researchers”, in Journal of Multilingual and Multicultural Development, page 10