Drew, with only one conversion, reducing the bids for mobile might not be the best way forward. You're getting the majority of the clicks from mobile and there's no reason why people would buy from their desktop rather than their cell phone unless the mobile version of the website or your ad makes it difficult to navigate/is unappealing. I would look at the CTR of each keyword and perhaps increase the bid on those keywords that have the higher CTR. What position are your ads/keywords and what is the quality score? These factors should also influence your bidding. Just my two cents.
Somewhat related: I’ve actually stopped advertising affLIFT to mobile devices with my paid advertising. While a good chunk of our members do use mobile phones to consume our content, a majority of our conversions actually occur on desktop. Interesting to find this data 😀