If you have to ask this question, it is a sure sign you are not sufficiently socially calibrated to interact with other people on an air-plane. I advise you to invest time into better understanding your fellow humans by learning about psychology.
Yelling would be an overreaction, likely leading to further escalation and diminishing the chance of achieving the goal of stopping the maladaptive behaviour. GP acted correctly to suppress the impulse, I guess in the end he did nothing, which is the next best course of action. Adults are supposed to treat the problem situation in a calm manner and implicitly point out the established social boundaries (this works better if your personality is more masculine than feminine): interrupt the talking person and get his attention, kneel down to the same eye level, state clearly what can be observed what he's doing (having a conversation, perhaps talking loudly), what the effect is (annoying the other passengers), and remind him that calls are not allowed by the relevant authority (flight crew). Firmly direct him to end the call right now. Throughout the conversation keep stern demeanour, keep eye contact and the same level of volume when you speak.
If he complies right away, then mission fucking accomplished, requite by showing approval (nodding, making a slightly more friendly face), or perhaps even something expressing gratitude if that's appropriate in your culture.
The argument "not on a call, this is FaceTime" in an attempt to shift away from the central point of the conversation. Do not let him pull you into his frame. Simply ignore this sentence, keep referring to the call as a call. If he's stubborn, or ignores you, or wants to have a quarrel, then it is okay to metaphorically lose the fight. Walk away and inform the flight crew instead, it's out of your hands now. In the end, it is a certainty that you will win, even if the talking person turns out to be highly neurotic or narcissistic and throws a tantrum.
Pointing out disrespect is not likely to work, the talking person has already shown he does not care. However, shaming is more likely to work, it is a powerful social tool and it is very much appropriate to use here. You could say that all the people around are affected (insert hand gesture here) and they do not approve of what the talking person is doing.
What should not be done is body contact other than touching the shoulder to get attention; trying to take the headphones or mobile device; talking down (literally and figuratively). Do not ask, beg or demand, instead use the appropriate word that comes closest do instructing or directing, use the imperative verb form in your language.