Hi Sue,
The phone's ring is played through the lower speaker, so the first thing to check is whether that speaker is working. I assume you can make phone calls, which says your upper, or earpiece speaker is operational. Can you hear things like YouTube videos when you play them? Does your headphone jack work? Can you hear sounds through your headphones? The audio should switch back to the speaker when the headphones are unplugged; if they don't that would indicate your headphone jack is jammed or damaged.
At this point it's hard to say whether the problem is in your speaker or your headphone jack; either one is a distinct possibility. The good news is that parts for the 6S are dirt cheap these days so you could easily replace both fairly inexpensively. Another argument is that you have to remove the speaker anyway as part of the process for replacing the lightning port/headphone jack assembly, so for an extra few bucks you could just pop a new speaker in there while you've got it out anyway.
Here's the guide you'd need to replace the lightning connector assembly; there's a separate guide for just replacing the speaker, but if you just stop at Step 32 the instructions are the same for both guides.
iPhone 6s Lightning Connector Assembly Replacement - iFixit Repair Guide
Here's the connector assembly for sale here on iFixit. I'd suggest the Fix Kit version since an extra 5 bucks buys you all the tools you need to do the job, plus the precut adhesive sheet needed to reseal the screen when you put everything back together again.
iPhone 6s Lightning Connector and Headphone Jack
And of course the listing for the speaker would be useful as well.
iPhone 6s Loudspeaker
iFixit is an excellent source for parts and tools; all their parts outside of batteries have a lifetime warranty and their store personnel are great to work with. In addition, you're supporting iFixit's mission to empower everyone to be able to repair their own devices. However, I fully understand if you need to economize; if that's the case those parts can be had for a song depending on your cost vs. quality vs. delivery times. Go do a search on Amazon, eBay or AliExpress; if you shop around you can get both parts for under $15 USD. Make sure you get the precut adhesive sheet as well; I usually buy a couple because they're easy to mess up; if you don't get them in just right the first time you can't really take it off and try again - I usually end up with a tangled ball of glue and am glad I have an extra so I don't have to wait to reorder.
So check out whether you have sound or not from the headphone jack and the speaker and let us know what you find.
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