To experience a great performance of Alexa with an Echo device, on iPhone, download Alexa app from the App Store. For that follow these steps:
• Launch App store on your iPhone.
• Sign in with your Apple account or Gmail account.
• After that search for Alexa. Then tap on the Alexa app in the search result.
• Click on install. It will start the download and installation process.
• When the installation is complete, connect Alexa with Echo device by suitable steps.
Hope, you are using Alexa on your iPhone. In case, you face any difficulty is above given steps, take help from Alexa customer care number. https://echodevicesupport.com/echo-alexa-service/