For when and where I read (outdoors and in bright sun quite often), there's no way a tablet or phone could replace an ereader for me. There's also no way I'd want to carry around a larger heavier tablet to read on, reading on a tiny 4" phone screen isn't for me either, and not to mention I'd probably not make it through a day of reading on either a tablet or phone as fast as the batteries drain.
So ereaders are definitely going to be a must have in my case until I can no longer see to read

. There's zero chance of a tablet or phone replacing it for me.