Three stars. Rated R. 96 minutes. With her cracked-black-pepper voice, elastic features and astonishing willingness to go there, Jenny Slate may be the closest thing her generation has to its own Lucille Ball. She’s bawdier, for sure; as she proved in her breakout feature, the 2014 rom-com “Obvious Child,” she utterly refuses to observe the traditional niceties, whether she’s making off-color jokes about abortion or airing dirty laundry in the most unsavory sense of that term. In “Landline,” she works again with Gillian Robespierre, who directed “Obvious Child” and, as in that film, wrote the script with Elisabeth Holm.