This information comes from Roland Quandt of WinFuture.de who wrote that ASUS experimented with a 10GB smartphone, but apparently due to size constraints they could not/did not move forward with it. It is unclear as to which phone they might have been experimenting with, but it’s not hard to imagine that it could have been the recently announced ASUS ROG Phone.
https://www.sammobile.com/2018/06/07/exclusive-bixby-speaker-features
For those unfamiliar, the ASUS ROG Phone is a smartphone designed for gamers. This follows in the footsteps of companies such as Razer and Xiaomi, both of whom have launched smartphones aimed at gamers. To think that ASUS might want to put 10GB of RAM into the ROG Phone really doesn’t seem like much of a stretch, but it seems that they didn’t, although 8GB of RAM is admittedly plenty already.
In any case we wouldn’t be surprised if in the future we might see more phones with 8GB or 10GB of RAM, but one has to wonder if we might have gotten to a point where we might actually have more RAM than we really need.