Calculate the Numpad Taxicab
Jelly, 11 bytes

o-1.’d3ạ/ḞS


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How it works

o-1.’d3ạ/ḞS  Main link. Argument: [a, b] (list of integers)

 -1.         Yield -1.5.
o            Take the logical OR of a and b with -1.5.
             This maps 0 to -1.5, and all other integers to themselves.
    ’        Decrement the results.
     d3      Divmod; compute quotient and remainder of each result divided by 3.
       ạ/    Reduce by absolute difference across columns.
         Ḟ   Floor; round all differences down to the nearest integer.
          S  Sum; add the rounded absolute differences.