As a photographer, I want to correct you. Camera sensors are good, actually amazing for their sizes. What sucks is the lens + the sensor size combination. On most phones you get a fixed wideangle lens, some phones have two lenses, some have sucky zooms (Galaxy S4 Zoom). None of them come even close to a cheap DSLR/mirrorless with large sensors. All 100% of the phone cameras suck in low light. Yes, even the latest iPhone and Google Pixel.
Phone cameras are orders of magnitude worse than the cutting edge cameras when it comes to light sensitivity. It's just physics, there are only that many photons falling into the lens.