I have a cheap aluminum bottle cage hanging from my handlebars. I used an inexpensive connector from the bike store that works great. My bike has a bottle cage, but it is in use to hold my foldylock.
My phone carrier is, um, my pocket. If I'm riding on a new route and need to check the map, I pull over which serves both a map-checking and a resting function. Works for me. Usually if I'm on an unfamiliar route it is recreational, or prep for using that route for an errand or commuting on another day, so no time pressure.
My husband, meanwhile, has one of those zipper type phone cases that displays his phone through clear plastic. He is happy with it, but the downside is that he sometimes forgets to take off the phone from the bike. The upside of that is it provides a bit of sprinting to round out the exercise gained via the ebike outing.