Absolutely yes you can load it to the app and still use the physical tickets if you wanted to conserve your battery.
We actually use our phones most of the time now though since both my husband & I have loaded all of our passes to each of our app’s. That way we can have tickets on us all the time & separate & park hop or what have you without having to worry about someone needing their physical pass. To keep at sufficient charge level we try to always start each day with the phones fully charged as well as a fully charged external charger. We can then get two good charges each with the external and it allows us to freely use our phones since it totally eliminates our fumbling for tickets when redeeming our fastpasses, entering or re-entering the parks. I
If you elect to add MaxPass to your tickets you wouldn’t even need the physical tickets to pull FastPasses. We don’t have MaxPass added to our annual passes so this is where we need the tickets the most & for that I just keep them in a wrist wallet that I keep separate from my day to day wallet & only use in the parks. It’s only big enough for my phone and a few cards so it only holds our physical passes, any paper fastpasses we need to keep on hand (like for the shows), one credit card (and/or gift card) plus my ID.
Before I had the wrist wallet I always had one designated pocket for the tickets but then I had to make sure whatever I wore had a pocket and sometimes a girl wants to wear a skirt to the parks, plus women’s pockets are extremely tiny so I was always so paranoid about everything falling out. And I’ve lost a fastpass or two when I haven’t been able to pay attention. So I am a big fan of it being on my phone, leaving me one less thing to keep track of