throw a party

معادل give a party
مهمانی دادن و گرفتن

I had been planning a party means that I had already decided to have a party and I was working on the plans.
I had being planning to throw a party is an incomplete thought. It makes the listener ask whether it happened or not, or what you are going to say next to complete the idea.
For example, I had been planning to throw a party so I ordered a lot of food. Or, I had been planning to throw a party but I couldn't come up with a date that work

پارتی انداختن : مهمانی گرفتن

مهمانی برگزار کردن
ترتیب دادن مهمانی