In short: your average user probably doesn’t know of the existence RAM while they know about the existence storage memory, so the term memory is unambiguous to them.
The average user probably won’t know of RAM, because smartphone operating systems usually manage the RAM for the user. They also seem to have very few mentions of RAM in the operating system in general, since it’s none of the user’s concern. The average user doesn’t worry about possibly running out of usable RAM.
Users usually know about storage since it is at least partly managed by the user. Phone operating systems usually ask the user to free some space if storage space is running out. Applications also seem to mention to the user that they are out of storage space and there are tools to manage storage space downloadable or integrated in phone operating systems.
On the other hand, your average user won’t download an alternative operating system on your phone and install it.
Personally I always think of storage as non-volatile memory, while memory implies volatile memory for me.