Javascript Generate 7 digit phone numbers based on chess pieces

I am have a hard time coming up with a solution for an algorithm on hackerrank,

The problem

The following diagram is of a standard telephone keypad. It consists of a 4x3 grid of buttons. Using the valid moves of a piece from the game of chess, varying combinations of 7-digit phone numbers can be derived. For example, starting in the upper-right corner (the "3" key) using a rook (which moves any number of spaces horizontally or vertically), one valid number, after pressing the initial "3" key, is: 314-5289

1 2 3
4 5 6
7 8 9
* 0 #

Write a program that will count the number of valid 7-digit phone numbers that can be traced out on the keypad for every given chess piece. The following rules define a valid phone number: Seven digits in length Cannot start with a 0 or 1 Cannot contain a * or #

What i have tried so far

function find_positions_to_move(board, partial, row, col) {
    rows = [-1, -2, 1, 2, 0, 0, 0, 0];
    cols = [0,   0, 0, 0,-1,-2, 1, 2];
}
    positions = [];
    for (i in range(len(rows))) {
        if (3 > (row + rows[i]) >= 0 && 3 > (col + cols[i]) >= 0) {
            positions.push(((row + rows[i]), (col + cols[i])));
        }
    return positions;
    }
function recursively_generate(board, i, j, partial_result, max_length, result) {
        // if size if partial result is equal to expected length, then add partial result to final list of results and return
    if (max_length == len(partial_result)) {
        result.push(partial_result);
        return;
    }
    positions = find_positions_to_move(board, partial_result, i, j);
        // for each possible position add it to partial result
    for (x, y in positions) {
        recursively_generate(board, x, y, partial_result + String(board[x][y]), length, result);
    }

function generate_phone_number(board, start_i, start_j) {
    result = [];
        max_length = 7;
}
        // start with position start_i and start_j
    recursively_generate(board, start_i, start_j, String(board[start_i][start_j]), max_length, result);

Any tips on solving this would be highly appreciated. Thanks in advance