I took me months to figure out what that funny click buzzing sound sound was every now and again while I was flying. I would be much more interested to assure that the pilot using the phone as either a phone or a camera, was also being an attentive pilot, than to worry about the affect of the phone signals on the safety of a VFR flight.
I'm sure your instructor will fly while you take photos, and thus you can keep your eyes on the road while you're flying. Remember, you're spending your hard earned money to be up there flying, not riding, get as much flying time as you can! If you want to sightsee, deal your way into the back seat of someone else's lesson, then invite them to do the same on yours. You'll also get to learn from their mistakes - and them from yours!
Fly safely and have fun!
Pilot DAR