If the pillow top mattress is a one sided pillow top mattress then yes you can flip the pillow top mattress over but the other side won't be as comfortable as the regular side you sleep on.
The other side of the pillow top mattress doesn't feel very good to the touch because it's a non skid surface and it doesn't look as good being flip over.
However there's nothing wrong with flipping the pillow top mattress over on it's other side if you want too do so.
If it's the kind of pillow top mattress that has both soft top and bottom sides then you can flip those over as well and have a comfortable bed.
You can also just spin the mattress around which helps to save wear and tear on the pillow top mattress without the need to actually flip the pillow top mattress over.