Complex sentence: She doesn't get along with Darrin's mother, Phyllis Stephens (because Endora gets along too well with Phyllis' husband, Frank), but they are civil to one another in, what Samantha calls "killing one another with kindness".
Split into simpler sentences: She doesn't get along with Darrin's mother, Phyllis Stephens, because she gets along too well with Phyllis' husband, Frank. But, they are civil to one another in, what Samantha calls, "killing one another with kindness".