Does the flash from smartphones emit any UV light?
No. Hard to extend the answer with more details here... White is commonly composed by combining blue light (450-470nm wavelength) with phosphor. Phosphor converts a part of the blue light to yellow light (580-590nm wavelength). read more
LEDs do emit very small quantities of UV light but much less than CCFL lights. In addition there are losses through the layers of LCD and many displays also have filters to block unwanted wavelengths. read more