A replica is essential a node in the DFINITY network (just a different name). For DFINTY every node has to meet a certain hardware standard which is initially set by the foundation, this standard is way above of what a high-end smartphone could provide. Apparently you won’t be rewarded for your computation on the network (or even punished) if your performance statistically deviates from the other devices in the network (which would be the case if you would use a smartphone as a node).
Afaik what Ori is trying to say with edge computing is, that you take the computation to the “edge” of a network. So instead of calculating some stuff on a server and then sending it back to your smartphone, some of the computation could happen right on your smartphone directly.
To quote Andreas Rossberg (Co-Founder of Wasm):
Wasm (yes, correctly spelled without all caps). As you may be aware, Wasm is a newish low-level code format that aims to be portable, safe, and efficient.
It is currently supported by all major browser (yes also on your mobile) and you can also use it in your frontend code that is hosted on the Internet Computer, thus being able to “edge compute a little per app”.
Hope this helps!