Thank you for all your thoughts and ideas. After my turning the manual button on/off and turning the phone on/off/on, all the sounds came back several hours later!
So, it spontaneously reset, and it all works now; no idea why.
Here are my responses to your questions about the Do Not Disturb setting:
I do not have a schedule set that turns on Do Not Disturb and the "Scheduled" button is not on. My "Allow Call from" is set for everyone.
I was able to hear all of the various Sounds for text, etc., earlier today, only when I used my earbuds. Otherwise, the only sound that worked was when I received a call.
In the "Do Not Disturb" screen, it says under Silence:
"Only while iPhone is locked" is checked; not "always".
My screen was not locked when I received the phone calls, so I assume that the check next to "Only while iPhone is locked" was and is working.
These intermittent issues drive me crazy, and I'm just thankful that it all "fixed itself".
Again, thank you for all your support. I really appreciate it!