The phrase originally came from secular Palestinian nationalists in the 1960s calling for a democratic secular state within the boundaries of what was the British Mandate for Palestine, encompassing Israel, the then-Jordanian controlled West Bank and the then-Egyptian administered Gaza Strip — that is, the lands between the Jordan River and the Mediterranean Sea.
The PLO of that era also advocated mass expulsion of Jews and their descendants except those who lived in Palestine before the late 19th century, and even that was ambiguous, so I don’t know that “The phrase doesn’t have any connotations of ethnic cleansing!” is really correct here.