Is this inside your car? Or is it receiving direct sunlight angled with the face of the panel directly at the sun? Some cars have tinted or low-E glass that can greatly diminish the solar
radiation to the panel. I've seen some people think that just ambient diffused light will generate the power listed on the marketing materials which is always a stretch under the best of cases, with almost any panel. If it's just sort of "catching some sun" then it may generate a very small amount of energy. If your phone is powered on, that could just be enough to slow the draw rather than push a charge. The panel also looks like is has some surface damage on what I imagine is plastic covering. It is possible to create microfractures in the fine connections that will drop those areas from generating power as well.

I have one of these and I put it on my windowsill or on the dashboard and I have kept my phone charged for a week or more with just this: https://www.amazon.com/Wireless-26800mAh-Riapow-Waterproof-Flashlight/dp/B081C5TY2J/