Echo with iPhone 8 Plus IOS 11.4.1 and Toyota 4Runner 2018: have reset phone, reset audio in vehicle, deleted and re-installed. Have latest update on phone and in vehicle.
Cannot understand callers. Bluetooth is unusable.
Did you talk to your Toyota dealership for known issues—this may be most informative.
To do your due diligence user troubleshooting is follow the 3R's- if a restart does not solve your problem proceed:
1. restart, ie power off/on,
2. reset http://support.apple.com/kb/HT1430,
3. restore from backup, restore as new device. http://support.apple.com/kb/HT1414