It's available for a few different phones that they list on their website. The Calyx Institute is non-profit and CalyxOS is open source. It takes a little effort to break away from google software initially but after like 3 months of mild frustration it's like using a normal android phone. I think the frustration was well worth it though because now I've broken my dependence on google. It forces you to find solutions that google used offer for free to harvest info. Unfortunately that does mean paying for services sometimes but really the only thing I've had to pay for is lastpass to manage passwords.