I believe echoing is from the volume being too loud. Driverspeak is a great thing to check. The mic may be too sensitive.
Personally, I find talking on the phone in the 2016 a bit of challenge as the signal seems to rarely be strong. Don't know if it's the super quality of the build causing this, however it may be time to invest in a good wilsonamp signal booster.
Being a software guy... the echoing shouldn't be happening period on a standard call... it's digital noise cancellation 101. I can only guess that it has to be one of a couple of things.
1. BT is connecting audio output and not audio input, hence the mic the phone is what's actually being used, not the one in the car.
- this wouldn't surprise me since I haven't seen an update since the iPhone 7 was released (and that's the phone with the issue).
2. There is some kind of echo actually happening - like driverspeak which delays speech for the rear passengers.
- this seems like it would be odd; as I would think driverspeak would be disabled while in a phone call - but I've seen crazier bugs.
3. Is it caused by both parties being on speaker phone and the natural delay of cellular. I'm actually surprised at the amount of delay.
As far as signal - do you have an aftermarket window film installed? Metallic films (as opposed to dyed or ceramic) will hamper all radio signals. Additionally if you're keeping your phone in your pocket - the signal will also be lessened. Otherwise - I've not experienced issues with signal strength - if anything it seems actually better than other cars I've been in.