Hi @BertG
The Aperture increase is so small that I consider it negligible in regards to the claim
“Here, four pixels are combined to form one large superpixel that captures four times more light while being friendly to your phone’s storage (equalling 12-megapixel photos).”
Further the increased size of the sensor is not the same as the increased size of the lenses each pixel has, if there is any space between the pixels it may well be that needs a larger sensor area as there are now 40 millions to separate.
And of course there’s the diameter of the lens as primary aperture as the f/1.79 etc relates to the focal length of the pixels from the lens and if the pixels are smaller and shallower then each may be further from or closer to the lens.
The f/1.8 to f/1.79 change shows the overall increases in light reaching the lens, as I said before, is negligible.
"Each f-number is represents one “stop” of light, a stop is a mathematical equation (which is the focal length of the lens divided by the diameter of the aperture opening) that determines how much light that enters the lens regardless of the length of the lens. Such that an f/4 on a 50mm has smaller opening than an f/4 on a 200mm, but an equivalent amount of light travels through both lenses to reach the image sensor thus providing the same exposure."
Fairphone’s claim that four times as much light is available as a consequence of the 4 times increase in number of pixels shows either a totally inept expression by an monitored person or a total disregard to advertise the product as it really is.
I will at some point paint my view of this issue directly on Fairphone’ door, but currently they have more serious issues to deal with that camera issues 
It may be a 48Mp sensor but it acts as a 12Mp with little difference in output, specifically in terms of light absorption.