Don and Phil breaking up -- one may entertain cruise passengers (7)
I believe the answer is:
dolphin
'one may entertain cruise passengers' is the definition.
(a cruise ship might pass dolphins)
'don and phil breaking up' is the wordplay.
'and' says to put letters next to each other.
'breaking up' indicates anagramming the letters.
'don' after 'phil' is 'phildon'.
'phildon' anagrammed gives 'DOLPHIN'.
(Other definitions for dolphin that I've seen before include "Sea-mammal" , "Small toothed whale, larger than a porpoise" , "Sociable sea mammal, sacred in ancient Greece" , "Marine mammal with an elongated beak-like head" , "swimmer" .)