No, "using a radio/field phone" is explicitely listed as an action that are not causing loss of concealment. The same is true for a Spotter, or a Gun that has no GO enemy units in its LOS.
So the usual course of action is to place the AR, and if you're in doubt about the LOS: Tell your opponent to look away while you check the LOS. If the LOS is OK, you go on with the OBA, if not the Fire Mission is cancelled.
You'll generally do it the same way for Spotters or Guns firing at non-GO enemy units. It's really fun to fire a Gun at your enemy's broken units, without placing the Gun onboard or even indicating from where you're firing. It makes your opponent quite nervous :devil: