People say my voice is garbled when using my iphone with or without speaker on

If you have a hearing or sound issue on your device then please try some of these processes to set it right

1. If you have a distorted sound issue on your iPhone --> If you hear no sound or distorted sound from your iPhone, iPad
2. If you are not able to hear the other person, click this...>If you can't hear a person on a call or voicemail or if the sound isn't ...
3. If you only hear through speakerphone mode --> If your iPhone is stuck in headphone mode - Apple Support
4. If the other person is not able to listen to you then please click this to identify the issue --> If the microphones on your iPhone, iPad, and iPod touch aren't ...

If the above options do not mitigate the issues then Contact your carrier and then Contact Apple Support

nedwa wrote: "It has the original battery. 86% max capacity"

Although 86% isn't too bad, the iPhone 6s was made between Sept. 2015-2018 — so the aging battery could be affecting performance. Consider having the battery replaced:

iPhone Battery & Power Repair

About genuine iPhone batteries

Repair Provider Verification

(Articles found by searching Apple's Knowledge Base.)

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nedwa ~ Does your iPhone 6s still have its original battery?

And what's the Maximum Capacity % here?...

Settings > Battery > Battery Health

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