The phone layout came from user testing at Bell Labs before Touch-Tone dialing was introduced. In a July 1960 Bell System Technical Journal study, R. L. Deininger compared 16 pushbutton arrangements and found that the layout used on ten-key adding machines, the 7-8-9-on-top order that calculators still follow, was not the best performer; the same grid with a different numbering was slightly faster (4.92 versus 5.08 seconds per number), and the three-by-three-plus-one grid was carried forward for its engineering advantages. Calculators simply kept the older adding-machine convention, so the two keypads have stayed opposite ever since. The study also noted that the speed differences between layouts were small, so neither order is dramatically faster.
Image: Western Electric 10-button WE 1500 Touch-Tone telephone, Telephone Museum, Waltham, Massachusetts. Photo by Daderot via Wikimedia Commons, CC0.