While it is not A5, this is only a "recommended minimum". If you can demonstrate to yourself it is suitable, it's fine. That's the way I read it.
I also questions their assessment the iPhone is not suitable as backup. IT'S A BACKUP! Used only if the main one fails, which is an extremely rare occurrence.
At the very least there should be a difference made between IFR and day VFR. Flying a plate from an iPhone on a stormy night probably isn't a good idea. For Day VFR, and iPhone plugged into ships power is all you need, especially as backup.