I fixed this and just had to post because I don’t see the answer here, it took me a long time, and I almost can’t believe what it was.
My phone: Moto G7 Plus.
Bear in mind I of course checked the volume button on the side and went into Settings and set the Ring Volume to high. I also tried almost everything else people mentioned (including dropping the phone(!) but not factory reset) with no solution.
Here’s what worked:
Playing with the volume button on the side of the phone, I tried pressing the weird icon below the volume indicator and below the musical note (it’s sort of 3 lines but some are like horizontal letter ‘T’s) and much to my surprise, a different Media, Call, Ring and Alarm Volume box opened up (!) and there the Ring Volume was slid down to Off.
Why the f that box isn’t synced to the other one under Settings so that if you change one you change the other I do not know besides the fact that it must be a fd up mistake because whatever positive can come from that can’t negate the negative which is that no one would ever the f think of that as the problem. I just got lucky.
But that’s done. Maybe it’s your issue too. Good luck.