I like the idea, but connecting a phone to an external USB drive seems ridiculous. A 1 TB microsd card costs well over €100.
You are probably going to kill your phone faster with this setup.
I don't think so, keeping it wall mounted makes it much less likely to drop it (which is how most phones break).
Get a used netbook and replace its hdd
I have several old netbooks, but they're limited to 1 or 2 GB RAM. That's makes Bitcoin Core very slow.
after watching a YouTube video about Apple's ARM chips, they (and other recent ARM processors) will *probably* have the required CPU performance to run Bitcoin Core, but memory is still a question mark. Disk is obviously a no-no of course.
My current Android phone is 2 years old, and was high end. It has 8 GB RAM and I'm pretty sure both the storage and CPU are much faster than my old netbooks. Possibly also faster than my (aging) laptop.
The main problem I see with this is the cost: powerful phones with enough storage are still expensive. I do have a pile of old phones that I don't use, but those lack performance. Give it a few more years, and many people will have old phones powerful enough to run this. Throw in $20 for a 1 TB microsd card by then, and it's a very cheap way to run a low-power node. So give it time