One thing about the technology industry is it goes through dynamic changes. So just because something might have been true at one point in time does not mean mean that it will stay true forever.

I wrote about computer filing systems a number of years ago were I spoke about temporary vs permanent storage. In in those days, temporary storage was what was called RAM (Random Access Memory) and permanent storage was typically on computer hard drives.

Temporary storage was where things happened temporarily, before being saved to permanent storage. Like when you create a document than later save it.

Today even though the terms RAM and hard drives are still used, the distinction is becoming far less obvious. A better terminology is to use what's called volatile as opposed to non volatile memory or storage.

Volatile memory or storage is where when the electrical power get switched off to the device, data is no longer stored. Non-volatile memory or storage means that no electricity is used to maintain the storage. No electrical power is required to maintain non-volatile memory.

As I said earlier, non-volatile memory used to be computer hard drives. Because of advances in technology, non-volatile memory has been, for many years, memory sticks or pen drives and more recently SSDs (Solid State Drives). The reason that have been given the name, “drive” is because they have replaced hard drives. However the name is inappropriate from the point that hard drives were a mechanical, driven, a platter spinning around,driven by a motor. SSDs and memory sticks are not mechanical at all. Ther is no motor no platter and nothing spinning. They are not driven mechanically at all. Hence they are much faster for both saving and retrieving data than a mechanical hard drive.

Ther are different types of solid-state, non volatile memory. The distinction between them appears to be the speed at which information can be written or read from the memory. As technology has advanced the speed has increased.

Mobile phones which in reality are basically pocket computers, run on batteries,so tend to use all non-volatile memory. That way they don't have to use electricity to keep the memory alive. So the battery last longer than what they otherwise would. This memory is both what was typically called RAM in the past as well as what was typically called hard drive storeage. So in theory, phones do not lose what's in temporary storage when they are switched off or have electrical power removed.

Computers also have non-volatile storage. SSDs. I am not aware if they use non volatile RAM.

All the above is how the hardware works. Then there is software.

For many reasons the software and particularly the operating system software on phones works differently to that of computers.

Because of the solid-state design of phones and so the speed at which they work, it is difficult to determine if phones maintain data in RAM when completely switched off or have no electrical power going to them. Another problem in determining if phones can keep data in RAM when they switched off is the concept that when a computing device is switched on the possible need to start everything from a given point. If phone's or any computing device,for that matter, were never booted up there would be the possibility that corrupt data could not be removed.

I am therfor unable to determine if phones do keep there solid state RAM alive when they completely powered off.

However i know that if i have multiple tabs open in a browser and I power my phone down, switch it off completely, it still has all the browsers tabs available to me when I restarted it. However this could be because it has been written to more permanent storage.

However on my android phone a test of creating a simple text document and not saving it and then powering off the phone, I was not able to see the non saved document when I restarted it. It is possible that you phone operating system cleared what was in RAM before it started or when it shut down, for security reasons.

My point in writing all this is to show that just because something happened because of certain technology in the past i.e. computers, does not necessarily mean that applies to the newer technology, i.e. on phones.

Detailed discussion about volatile VS non volatile, memory

https://superuser.com/questions/638675/why-does-ram-have-to-be-volatile/638809