There might be no confusion, but if an airfield is PPR (leaving poor grammar aside) it does make a difference whether it is by phone or by radio. If you're airborne and you decide to fly in to somewhere (perhaps not for a "real weather diversion" but an unplanned stop - you need a break maybe) then you can't call, so you care about the difference and so it's helpful if the flight guide makes the distinction. Of course, nothing to stop you trying on the radio if it's not clear. Unless of course you're thinking of dropping to Elstree without phoning and you get flustered if you get a bollocking on air.