Do I have to bring my reservation details when I check in at the hotel?

pu1. You don't have to

2018-12-04

OK

pu2. You can just show it on your phone

2018-12-04

OK

pu4. It'd be nice to print it out and show it to them

2018-12-04

OK

pu5. You can also use it on your mobile

2018-12-04

OK

pu6. There's a hotel that sometimes talks about reservations differently.
It's a big hotel, but it's like that
So I tend to print it out

2018-12-04

OK