Inflield Fly how to "declare" one

[lc_huxter]

Another umpire and I were discussing the inflield fly rule. He stated just by pointing in the sky should be good enough to declare an infield fly.
I on the otherhand disagree with him. I refered to OBR where there are two types of infield fly. One if it is fair and the other if it is foul. If OBR wanted us to say "Infield fly if fair" how can a finger pointing in the air declare that statement?

We also disagree on the infield fly rule. I say it is not an automatic thing. It is a judgement call, so if we do not "declare" it then it is not so. Is this true or is it automatic?

Thanks