It's currently impossible to answer this question as a blanket statement because everyone's needs are different. Plus, a lot of people now have multiple devices: a phone, a PC, and a tablet. These devices all serve different purposes.
Let's take up my personal array of devices and needs as an example. I have a desktop which I use for 3D modeling and gaming. I have a Surface 3 for on-to-go basic computing and for inking music in OneNote. I have a work laptop which is primarily used for Office tasks and the occasional use of Visual Studio. I also have a Windows 10 Mobile device.
Assuming the device can make calls and easily fit into my pocket, it could replace my phone.
Assuming it has some Continuum capabilities, it could replace my work laptop on days when I don't need Visual Studio. So if I work from home on a given day and know I'll be in Office all day, I could use that the whole time.
If the device is large enough or can connect to a Continuum device that meets my needs, it could replace my Surface 3.
As mentioned, it won't replace my desktop.
The real question is what can the device do as well or better than a PC, phone, or tablet and in what situations. Context is also hugely important. Take PCs and tablets. A lot of people have both. Smartphones just add texting and calling capabilities. Looking at just PCs and tablets, why do so many have both when a PC can do pretty much everything a tablet can do? Because context matters. I might need the power of a gaming desktop but also need the portability of a tablet for when I'm on the road. Adding phones to it, I might need a simple laptop for writing long college term papers but I also want a good phone so I can run the latest apps for communicating with friends on the go. In what situations will this device be able to replace a PC or tablet with little to no compromise?
Here's a shift in technology that I think is akin to what might happen with Andromeda and therefore can provide some perspective: The MP3 player. The standalone MP3 player has basically gone extinct. Look at Apple's homepage. The iPod isn't even listed in their top bar of devices. But we didn't stop listening to digital music. It's just that phones reached a point where they could replace the MP3 player. In the past, phones didn't have the capability of playing music, or they required goofy dongles that made it a pain, or you had to buy special headphones to do it, or playing music drained the battery too much and there was no easy way of charging on the go. All of these roadblocks are now gone (although Apple is bringing back the dongle to some degree) and new value has been added. You no longer need to connect to a PC to add music. USB ports for charging are starting to pop up everywhere. The MP3 player has been replaced and it was merged into another device. So how will Andromeda replace and build on what's already out there? We'll just have to wait and see.
But it all comes down to what the device costs, what it can do, and how well it does it. Until we know that, it's all just speculation. I will say though that the device alone without any Continuum like capabilities (connect to a dock or shell and make it more like a laptop/desktop/tablet experience), I don't see it making any waves or replacing anyone's computer or tablet.