My iPhone auto shutdown and restart

Hi,

Your iPhone may not have the battery capacity to keep running at a low battery percentage. To check if it was the battery that caused the shutdown go into Settings > Battery > Battery Health then look for a message that roughly says that your iPhone recently shut down due to not having enough power. If this is the case you will need to get your battery replaced. If this is not the case and it happens again, take it into an Apple store (when its open) and have it checked.