Many of us photograph with phones and even with actual camera devices (compacts and DSLR:s) in everyday situations automatic settings are used. On phones, they are used practically exclusively.

Automatic settings have a really hard time being accurate with skin tones. If you want to photograph skin tones with decent accuracy with automated settings, this is your best setup.

1) Pick indirect daylight for your lighting. Heavily overcast day OR a preferably north-facing room with large windows and no artificial lighting on at all are your best options. If direct sunlight comes into the room, wait till it does not – or if the room is large enough there might be an area where the direct light does not interfere.

2) Neutral background. Neutral mid grey is the best option, but black, white, and other neutral greys will probably work, too.

3) On the picture composition, make sure that there is quite a bit of that neutral background included.

4) Subject should not wear any crazy colors. Neons and other brights really mess up some automatics.

Also as a footnote, many phones do heavy processing for the images automatically. I'm afraid that some of these processing algorithms might also include something to "optimize" pleasant skin tones. If you feel that your phone camera does not capture the skin tones as you perceive them, it might be useful to look into some separate camera apps that give more control over the settings and processing.