It's either bad hardware or bad software.
It's not necessarily liquid damage. But it is some kind of fault with the built-in sensor. Possibly mechanical (blocked or jammed by debris, coated in gunk, whatever), possibly electrical (broken solder points or intermittent electrical shorts, whatever).
You can hard-reset the device so it restores all softwares to factory default.
After you backup or copy everything you want to keep (contacts, numbers, messages, photos, passwords, browser favourites and history, etc).
You can try cleaning "debris" out of the USB/charge port with tweezers. Or scrub it with a Q-tip coated with an electrical contact cleaner like DeoxIT, Stabilant-22, or isopropyl alcohol ("electrical-grade" or "anhydrous", not common drugstore stuff because they often have perfumes or additives which can leave an electrically conductive or electrically insulating residue). You can also try cleaning it with compressed air or with a vacuum, little to lose if it's already failed but it does risk of somehow making it worse or breaking other delicate mechanisms.
Remove the battery first, of course, just to be safe.
If it continues to malfunction then you may have to replace the USB/Charging port. Or have a repair shop do it for you. If it's not too old then it could be covered under warranty, or maybe you can return/exchange it. iFixit likely offers everything you need if you choose DIY repair.
@Anonymous 's advice is also good.
Be certain it's not a bad USB cable or USB power source (charging block, computer port, etc) before you do anything to your phone.
