Hi!,
1. going to - because it ´s more of an intention(phoning would mean more that it wasn ´t planned for tonight)
2. going to - again because it ´s an intention, but no real plan has yet been made, with concrete dates etc
3. I ´m meeting - because it ´s an arrangement (planned, organised, fixed)
4. going to - because it ´s an intention, THOUGH it is one of the cases where you could use buying, though because it ´s being reported I ´d say you are reporting someone elses intention.
5. going to - again, intention is more the implied question, but "doing" could also work if plans have already been made....for example the person asking the question could you going to (to enquire about future intentions) but if the responding person has already found a placement or job, they could reply with Present Continuous (because it ´s a fixed plan)
6. going to - you can ´t say someone has PLANNED not to enjoy the party. GOING TO is the only correct one here, it ´s more like a prediction (therefore will could also be used - you won ´t enjoy the party next Friday). E.g. I think it ´s going to rain tomorrow.
hope this helps!
Good luck
