The root system is likely to be as big as the bush, with a really deep tap root, so it'll probably be one heck of a job to dig it out, and to dig a big enough hole for it in the new place. Don't try to move it at this time of year, spring is the recommended time for this. You'll need to cut the branches back by about 1/3 and keep the bush well watered for quite some time after moving.

I think a better plan would be to take some cuttings from the original bush. They root really easily - a neighbour gave me some "sticks" from her Philadelphus last year, I rammed them into a shaded piece of ground and about half rooted with no fuss or bother, or extra care or attention. They just grew.

If you google 'philadelphus pruning 'it tells you very clearly there to prune off flowered shoots to one third length and 1 in 3 old shoots to near the ground. If this is done each year it keeps the bush tidier, as it gradually spreads and gets out of control. We eventually got rid of one that hardly bloomed.