TRY TO LAND FEATURED SNIPPETS.
Another way to rank for voice searches is by having your pages show up in featured snippets. When we're talking about pages, we mean all of the pages that aren't your FAQ page.
Now, the relevance of featured snippets remains a highly-debated topic since Google's deduplication update. However, they still are helpful when it comes to Alexa, Siri, or Google Home reading out results.
According to Google, if you don't have featured snippets, you won't be able to rank for voice search queries at all.