Q: "Date format" conflict between iMac and iPhone

hi all,

  Using Apple Numbers for iCloud.  By referring to a previous date such as "Jan 17, 1994" in the formula DATEDIF("1/17/1994";now();"D"), the result

in the iMac is Ok and in the iPhone is  ERROR.

But in changing the "date format"  in the same formula like  DATEDIF("17/1/1994";now();"D"), the result in the iMac is ERROR and in the iPhone is Ok.

Thanks for any help