Say i buy all of the parts one way or another to build a smart phone, not a custom phone but a existing phone say a Samsung Galaxy S4 or Sony Xperia Z2 could i actually make this, so to speak work in full functionality?
No, requires soldering, intrecate connections, working on micro level to connect them properly, phone is not like a computer which you can custom build, you won't be able to put everything on PCB w/o damaging some component.
Depends on what he means by 'all parts'. If he's on about everything from the individual capacitors and such to the connectors, all as individual modules then yes, it's basically impossible without spending a fortune on the correct equipment. However If he simply means buying 'spare parts' and assembling them then yes it's completely possible. More expensive overall but possible.
Say i buy all of the parts one way or another to build a smart phone, not a custom phone but a existing phone say a Samsung Galaxy S4 or Sony Xperia Z2 could i actually make this, so to speak work in full functionality?
It's possible sure. Same way if you buy all the parts for a Boeing 747 it's possible one way or another to build it in your backyard. You just need to know how.
Simple way to try it, buy a phone, break it down to as many parts as you can and put it all back together.
No, requires soldering, intrecate connections, working on micro level to connect them properly, phone is not like a computer which you can custom build, you won't be able to put everything on PCB w/o damaging some component.