I'm not a particularly tech-savvy person, but with certain things saved to the "cloud," what's entered in one device shows up in another. With apple products, one can also transfer items with an "airdrop" between devices. For my end, I keep everything on my ipad. I've worked with various EFB setups, involving ipads and other devices. The easiest setup I've used was the same ipad in a fixture in the airplane, that I had in the hotel, so no need to transfer anything; when I got my flight release at the hotel, I did everything before I left the room, and when I got t the airplane, that ipad slipped into a bracket and was the chart source and EFB I used in flight.
I do have .pdf expert on my phone and ipad, so can transfer items that way, and there's a cloud transfer or storage that can be used, too. The setup I have right now is my own ipad, but a different device in the airplane. I reference the flight release that I've been sent, on the ipad, and I carry that in the airplane, but I don't transfer it to an EFB on board. I can receive it or see it on my phone and my ipad, but a phone is too small for looking at most anything, so if I'm going to mark it or review it, it goes to the ipad.