Most houseplant problems come down to light. Point your phone camera at a spot and get a reading — plus which plants will actually be happy there. Everything runs on your device; nothing is uploaded.
Point your camera at the spot where the plant lives — a wall or the view it “sees” — and hold still for a couple of seconds.
Hold the phone where the plant would sit, camera facing the same way the plant would “look” (usually toward the window), and keep still while it samples. Take readings at the same time of day you're usually home — light in a room changes hugely between morning and afternoon.
It's an estimate. Phone cameras adjust their own exposure, so treat the category as the useful part and the lux number as a rough guide. For borderline spots, measure a few times and go with the lower reading.
Tracking a plant? Add it to your garden and set its light level there so its watering schedule adjusts.