You will benefit from using a WordPress caching plugin on your amp website.
When I first started using accelerated mobile pages (amp) for my website, I didn’t think I needed a caching plugin because I thought that amp cache was sufficient, but it was not. Here’s why:
A cached version of your amp website is served to visitors landing from Google Search, and if they visit subsequent pages on your website, they are no longer served a cached version. The result is a longer wait time to generate the webpage because the WordPress PHP scripts are run, and the database is hit.
Whether your website is completely served on amp or partially, you will benefit from installing WP Super Cache.
WP Super Cache is the best caching plugin for WordPress websites because it is compatible with the WordPress amp plugin, and it is created by the WordPress contributor Automattic. Read more about the WP Super Cache.