I live in Texas. I think you are just confused about meaning of the word "contrast" because you keep using in a way that makes no sense for contrast but makes some sense for brightness. Contrast in this context is the ratio of luminosity between brightest and darkest areas of a display. For a non-emissive display such as e-ink or LCD in a bike computer the ambient light level makes zero difference: the white pigment in e-ink will reflect/diffuse ~15 times more light than the black pigment in the same. Light areas in an LCD screen will reflect 1000 times more light than dark areas. The absolute amount of light above quantum level makes zero difference, it's the same for a candle, Sun or a supernova star - the ratio i.e. contrast remains the same. An e-ink display can be brighter than a reflective LCD though due to higher albedo, this is likely what you are talking about.
Also, if you really try to do what you suggested - you should not use an LCD phone, phones do not have reflective LCD displays but use backlight instead so the contrast on those decreases with increase of the ambient as both light and dark areas reflect the same amount of ambient light and the only difference is the backlight's emissive portion, the higher is the ambient, the lower of the ratio i.e. contrast.
Also, if you really try to do what you suggested - you should not use an LCD phone, phones do not have reflective LCD displays but use backlight instead so the contrast on those decreases with increase of the ambient as both light and dark areas reflect the same amount of ambient light and the only difference is the backlight's emissive portion, the higher is the ambient, the lower of the ratio i.e. contrast.