I have an iPhone and have downloaded the Alexa app (and uninstalled and reinstalled) many times. I went under the Cellular Settings and turned off WiFi assist after reading some articles about how that helped Androids and the app still freezes on the screen that says "amazon alexa" with the spinning wheel under.
If anyone has ideas I would love to hear them. I spent hours on the phone and emailing with Amazon Support and they can't solve the issue either. I have uninstalled, reinstalled, reset router, restarted phone... everything! My phone is updated and my wifi is working... but my Echo Dot remains unconnected.