Determine if Lat/Lng in Bounds

The simple comparison in your post will work for coordinates in the US. However, if you want a solution that's safe for checking across the International Date Line (where longitude is ±180°):

function inBounds(point, bounds) {
    var eastBound = point.long < bounds.NE.long;
    var westBound = point.long > bounds.SW.long;
    var inLong;

    if (bounds.NE.long < bounds.SW.long) {
        inLong = eastBound || westBound;
    } else {
        inLong = eastBound && westBound;
    }

    var inLat = point.lat > bounds.SW.lat && point.lat < bounds.NE.lat;
    return inLat && inLong;
}

This is a slightly optimized version of CheeseWarlock's Js answer, that short circuits.

const inBounds = (point, bounds) => {
    const inLat = point.lat > bounds.sw.lat && point.lat < bounds.ne.lat
    if (!inLat) return false

    const eastBound = point.lng < bounds.ne.lng
    const westBound = point.lng > bounds.sw.lng
    return (bounds.ne.lng < bounds.sw.lng)
        ? eastBound || westBound
        : eastBound && westBound
}

As you asked about both Javascript and PHP (and I needed it in PHP), I converted CheeseWarlock's great answer into PHP. Which, as usual with PHP, is a lot less elegant. :)

function inBounds($pointLat, $pointLong, $boundsNElat, $boundsNElong, $boundsSWlat, $boundsSWlong) {
    $eastBound = $pointLong < $boundsNElong;
    $westBound = $pointLong > $boundsSWlong;

    if ($boundsNElong < $boundsSWlong) {
        $inLong = $eastBound || $westBound;
    } else {
        $inLong = $eastBound && $westBound;
    }

    $inLat = $pointLat > $boundsSWlat && $pointLat < $boundsNElat;
    return $inLat && $inLong;
}