I have no problem answering my texts or phone calls but, if I am on a spooky horse, absolutely not. I always keep my phone on me whether it's in the arena on one of the posts or in my pants back pocket, either way it's on me.
My horse knows my ringtone and my text message, there was one time he RAN over to the phone because it went off. I also take it as a training experience, if your at a show and a cell phone goes off and your horse doesn't know what the heck it is, don't you know it could be a scary monster and come and get you?
But, if my horse should happen to spook while i'm on the phone, I have no problems throwing the phone down and correcting, I don't care who I am talking too. I also keep my phone on me at all times because, there is no one at my barn 99.9% of the time it's just me there and NO ONE else. Yes, the BO lives on the property and she can pretty much see what's going on if she looks out her window but, i'd rather have my phone on me.