You may need to keep the physical copy for it to be legal or moral according to your own ethics but from a purely technical standpoint there is absolutely no need.

Personally I hate using cash, especially coins, but going completely cashless is a terrible idea. My university’s canteen no longer accepts cash and I wanted to buy a coffee. So I tap my phone like I always do. Payment won’t process. Okay, so I try my physical debit card. Still nothing… Luckily a friend could help me out in the end but it would have been far less embarrassing if I could’ve just handed them a fiver.