For Phaser.Plugin.IsoArcarde, this helps displayObject placement by moving it above others. This is done by moving them up until they no longer overlap with anything.

placeAboveOverlaps.js

/* 
* For Phaser.Plugin.IsoArcard, this helps displayObject placement by moving it above others. This is
* done by moving them up until they no longer overlap with anything.
* @method Phaser.Physics.IsoArcade#placeAboveOverlaps
* @param {any} displayObject - The display object to move.
* @param {any} groupCollision - The the group of displayObjects to check for overlaps with.
* @param {number} [startZ=displayObject.isoZ] - The speed it will move, in pixels per second (default is 60 pixels/sec)
*/
function placeAboveOverlaps(displayObject,groupCollision,startZ){
    var overlap
    startZ = startZ?startZ:displayObject.isoZ;
    var deltaZ = displayObject.body.height+game.physics.isoArcade.OVERLAP_BIAS;
    var maxZ = game.physics.isoArcade.bounds.height;
    var isoBounds = displayObject.isoBounds.copyTo(new Phaser.Plugin.Isometric.Cube());
    
    /* Check if two sprites overlap */
    function spritesIntersect(displayObject,sprites){
        var overlap
        for (var i=0; i<sprites.length; i++){
            if (sprites[i].isoBounds && sprites[i]!==displayObject && displayObject.id!==sprites[i].id){
                overlap = displayObject.isoBounds.intersects(sprites[i].isoBounds)
                if (overlap){
                    return true
                }
            }
        }
        return false
    }

    for (var i=startZ; i<maxZ-deltaZ; i+=deltaZ){
        // move up and check again
        isoBounds.z=i;
        overlap = spritesIntersect({isoBounds:isoBounds},groupCollision.children);
        if (!overlap){
            displayObject.isoZ=i;
            displayObject.body.prev.z=i;
            return i;
        }

    }
    return i;
}