After multiple calls ( 6 opened case #'s to apple tech via phone) went into apple store for hardware check per apple tech senior advisor request. My phone, out of 4 new family phones, was the only one with the echo problem - on speaker, wireless earbuds, and car connection, and both I would hear echo as did other person on call. Here is report from Apple store & suggested to "REPROVISION "- which worked!!! 3 weeks of headache and waisted time GONE!

Problem Description/Diagnosis

Issue: Customer reports issues with audio echoing on calls ( started to place all details of tests done at store- but all turned out fine) Save yourself a trip to store and try this.

Reprovision is reconnecting SIM or eSIM in case of 15 pro.

Contact cell service provider and tell them apple tech suggested " need a Reprovision" of phone. Make phone call on different phone but make certain the Reprovision is occurring on your phone number. The Apple Store tech said this is a problem that was recently identified by apple. For some reason a phone will connect with a further cell tower and not get a solid connection. ( once get to correct cell carrier dept., process takes about 30 min) Good luck