You can download Google Stadia on any recent Android smartphone - while 'official support' is for most Samsung Galaxy, OnePlus, Google Pixel, Asus ROG and Razer phones, thanks to 'experimental support' you can use any other handset on the same operating sytsem.
That means, unless you have an Apple iPhone or really old Android phone, you're able to play Google Stadia, and thanks to the free trial, it won't cost you straight away either.