There's definitely some truth to this, but not a lot; the only phone number I remember is my own, everyone else's is stored in my phone which alleviates me from the task of remembering them. It's not that I forgot, I never learned these numbers to begin with, I didn't need to. It's no different from writing these numbers in a notebook and referring to this notebook whenever I needed a given number; I don't need to memorize these numbers so it's better that I don't, it'd be wasted mental space otherwise, and wasted time spent in memorization. To be fair however, this method I mentioned will likely lead to me remembering the numbers anyway, as I'd be punching them in every so often; the phone let's me skip this step as well. I only remember my own phone number because I inevitably have to give it out; similarly to the point I mentioned about remembering numbers I have to punch in, I remember mine because I often have to give it out.
I don't remember what I did on Monday because there is no need to remember these things. With or without digital devices, I wouldn't remember such minutiae. I can tell you what probably happened:
1. I ate some food several times
2. I worked on my projects
3. I went to the bathroom several times
4. I drank some water, and probably a soda, several times
5. I used the Internet at some point in time, probably to watch YouTube
There's really nothing worth remembering as to what specifically happened on this day. I know some people remember literally everything, but that's not everyone. What benefit is it to me that I remember what happened on this day? It's not because my phone stores this data--I don't consciously store any data on my phone about what I do each day--it's because it's not worth remembering. There are a ton of things I remember about my past, both recent and distant, but just another day in the life is not among those things. Maybe it's because my life isn't particularly interesting right now; perhaps if I spent the last week traveling, I'd remember my Monday more vividly.
They observe that people forget things, but don't observe whether people have always forgotten things which they don't need to remember. When they associate it to digital amnesia, they completely miss the idea that people have always stored relevant info, ever since it became easy and permanent to do so. Had people not done this, they probably would've forgotten what they wanted to remember anyway, or had to spend time and energy memorizing important info. Where's the digital amnesia here? There were no digital devices in the 1800's and yet people still stored information and forgot the information they stored--it's the whole reason they write it down, so they wouldn't lose it when they inevitably forget. Digital amnesia doesn't exist: it does not adequately explain this timeless phenomena, at best it's a trendy term for it. All that's been changed is the method as to which people record info.
It's obvious that digital devices, such as smartphones, computers etc. makes us more stupid, not clever.
Speak for yourself. It's all about how you use them. They're just like any other technology, just a tool. You were stupid or clever before ever approaching the tool, and the stupid or clever things you do with the tool are an extension of the self; self-degradation is a habitual choice, and so is self-improvement.